Riders Of Vision

I haven't dismantled the butterfly valve in the carbs or removed the shaft when I have done my strip and cleans.

However I do notice an engine idle change when I spray carb cleaner on to the throttle valve shafts, suggesting that I have leaking shaft seals.

I can't find these seals listed in the carb parts list at
http://www.yamaha-motor.com/partviewer/default.aspx?ls=sport#/Yamaha/XZ550RJ_-_1982/CARBURETOR/XZ550RJ_%281982_MOTORCYCLE%29/CARBURETOR_%28XZ550RJ_-_1982%29

Can anyone give me a parts number or suggest what to use to replace the seals?. Many thanks

I used little O-rings.

Check out the info posted here:  http://ridersofvision.net/rovforum/index.php?topic=6017.msg117298#msg117298

Yamaha never listed them . Their solution to leaking shaft seals is to buy new carbs!  Ya sure

Changing shaft seals is  not an easy project , The butterfly's are held in with tiny screws  that are staked. staking new screws is a perilous operation , as it very possable to bend the butterfly shaft,

Have not done this.  What about soaking the part of the carb body that the butterfly seals reside in with some type of solvent known to cause swelling in rubber?  Same concept as auto transmission and power steering stop leak products.  If imersing the whole carb body would cause problems for other rubber componets, perhaps a way of isolating and soaking just the butterfly seals could be contrived.

Really glad to see this discussion of leaky butterfly seals come up.  It's a problem that all our carbs either are facing, or will soon face.  High miles and old rubber are a double whammy.

I dip carbs in carb cleaner, for no more than 30 min.  This softens the seal a bit and cleans the carb, My policy is to NOT leave the carbs in the dip any longer , as the seals can be destroyed.

Thanks for the link to the 2007 discussion thread Cdnlouie, that was exactly what I needed. Not a job for thew faint hearted.
I like the notion of re-juvenating the existing seals whilst they are in place. Any suggestions for product that we might spray on while the engine is running so that the product is drawn in to the leaking area to 'swell" the rubber?

It is a great idea to replace these seals as they have all reached retirement age by now.  Some are still actually okay (I have an old set that are still good) if they have been in machines with regular use, but long term storage causes the rubber to lose some of it's elasticity.  These shaft seals have a very delicate outer edge that needs to flex in order to seal.  They are like the sails on a boat and when they harden they can longer catch the wind (vacuum more precisely) and press against the carb body to seal.  Regular immersion in gasoline actually preserves the rubber elasticity (apart from the downside influence now of ethanol), and once they shrink there is no coming back.  However, I  do know that varsol does causes rubber to swell (left a few o-ring pieces in too long during cleaning in the past).  I have never experimented with it on a shaft seal, nor would I recommend the process, but you asked  ;D.

FYI- Many carb dips will eat the rubber quickly. I believe there is a YAMAHA carb dip that is rubber safe. But most are not. Don't think even 30 minutes is safe. As a test I watched rubber o-ring desolve to uselessness in far less than 30 min.

Way back when I worked in a parts department I saw some monstrous things that the current carb dip did to various "rubber" parts.  The little gray cylindrical plugs that fitted between the cylinder fins to keep them from ringing would swell up to the size of a golf ball, some O rings would also swell to gigantic proportions. "Fortunately" we are now safer here in California, as the currently available carb dip is about as useful as dirty dishwater. 

I think that's the case across the board. All the carb dip products are much kinder/safer i.e. less effective. The Yamaha dip is literally "watered" down.  :o  It's sold in a concentrate that you must mix 2-1 water to product to make the final solution. I think the instructions indicate an hour dip but don't hold me to that. I used it in an ultrasonic cleaner for longer than that and everything seemed to be OK afterwards!

It depend on how crusty they are  . I usually dip them for as little as 10/15 min.  If there really bad I go up to Dream machines and use their glass beader. . Then I ahve to run them through the dish washer , twice ,to insure that there  is no grit left.

Rick, I'm guessing the stuff you use is what you may have found in a repair shop back in the day? Even if that's quite old and lost some effectiveness I'll bet it still works better thane the Yamaha dip. Fifteen minutes in the Yammy brand would do very little. I dare say one would get equal results by resting the carbs on a bench and talking harshly to them for a bit. A sound scolding indeed!  :D  :P  :laugh:

Rik, well sort of . I bought a 2 gallon can in WA. in 2003 , It was labeled "Not for sale in the state of CA,"  so i knew it would be good . I've been topping it off with the same brand (Berrymans)  here in AZ.  A couple of years ago the can started leaking , so I bought a porcelain stew pot and dumped everything it that . Its a bit taller and wider , which I like .

We ordered a couple of cans of carb spray and what we got was some kind of thin red oil, that did nothing. Turns out it was sent by mistake , it was intended for CA.  I'm glad I left there in '96!

Quote from: pinholenz on February 07, 2013, 05:42:05 AM
I haven't dismantled the butterfly valve in the carbs or removed the shaft when I have done my strip and cleans.

However I do notice an engine idle change when I spray carb cleaner on to the throttle valve shafts, suggesting that I have leaking shaft seals.

I can't find these seals listed in the carb parts list at
http://www.yamaha-motor.com/partviewer/default.aspx?ls=sport#/Yamaha/XZ550RJ_-_1982/CARBURETOR/XZ550RJ_%281982_MOTORCYCLE%29/CARBURETOR_%28XZ550RJ_-_1982%29

Can anyone give me a parts number or suggest what to use to replace the seals?. Many thanks

Hi pinholenz,

Throttle shaft seals on bikes this old should be replaced IMHO and anything short is just delaying performance and trouble free operation for years to come. You get one good shot for each screw so prep and diligence is key. An application of PB blaster or the like will help if the screws don't initially turn out easily, but clean the philips part with brake cleaner before you apply the screwdriver. Its all in the feel and even a slight tightening torque is what's needed to break them loose before unthreading. Also, a new or in top condition well fitting #1 phillips, attention to applied pressure so as to not bend the shaft or strip the heads, and attention to the staked part coming though the shafts threaded section (turn back in if needed to clear the threads and reduce jamming) is all part of the mix in negotiating the change out crux successfully. I've not had any trouble with the screws to date, but I also had carbs that were not in poor condition with lots of corrosion and such.

For my most recent replacement on a set of TDM carbs, I found a sweet set of metric counter sunk stainless allen screws at my local Ace. They're a perfect fit and a dab of loctite will set them well. Also be sure to put the seals in in the correct direction (V opening to the outside) so they seal with vacuum.

You'll need four of these 256-14997-00 (throttle shaft seals) direct from Yamaha. They fit many carbs on many makes... I forget the exact size at the moment.. 8 x 11.5 or something. They are listed on the old Yamaha XS650 twin fiche page. They're also cheaper in cost then the ones from aftermarket. 

Cheers,
Rich

I'm in full agreement with AdvRich.  Why go to all the trouble of carb disassembly, soaking, cleaning and reassembly without replacing the throttle shaft seals?!  ???  I've rebuilt several Vision carbs and always replaced the seals.  Not a big deal at all.  Some noteworthy advice - Use a #1 phillips for correct fit during removal/install.  btw...  The screws are actually "oval head" phillips and not a traditional countersunk.  Screws can be purchased from McMaster Carr under p/n: 90258A178, are M3 thread, 8mm long and stainless to boot!  Be sure to use a thread locker such as loctite #222 (designed for small screws and removable if needed) when installing the new screws.  Correct seals are easily obtainable from motorcyclecarbs.com by ordering p/n: 5599 @ $5.00 each.  The seal has an angled lip design and you must be careful to install in the correct direction.  Remember, you are dealing with vacumn and so the seals should be installed with the lip facing outward, away from the carb - Opposite from what you might think when installing a seal on an engine shaft or front fork tube.  The reward for replacing the butterfly shaft seals will be a smoother idling engine.  Well worth the effort!  Have fun and good luck.... :)

Oh... The screws from McMaster Carr are only available in packs of 100, so if anyone would like a new set of 4, (or more) just p.m. me and I'll send you some.  I'm sitting on a package of 100.  :laugh:

Great info and advice from Rich and Vintage - thanks guys!  :) Couldn't agree more, the payoff in overall fueling is well worth the little bit of extra work and expense. Also appreciate the part numbers/sources for seals and screws, good to know and I'll add to my list of reference info.  ;)

Rich, how confident are you in that Yammy seal number? It's listed (boats.net) for many models from 1970-2011 but I don't see XZ550 listed. Not that these parts finders are 100% accurate....  :( You've used them successfully? You are right about the price - seems to be nearly half of what motorcyclecarbs.com charges. This shouldn't surprise me as poking around that site I've been floored by their prices for everything. Hard to imagine a more exuberant use of the price gun than the OEM dealers but they've managed to do it.  >:(

edit: just occurred to me..price difference may be single lip vs. double lip design?

The improved idle (smooth) will not hunt or surge, making carb syncs easier too! Just "sayin."   ;)

Hi vintage bikeworks. Nice follow up. I made an adjust in my original post to emphasize the correct #1 size phillips. Loctite 222 is a good choice too.

Rikigun, Yes on the seals. They are 8 x 11.5 and the ones I used to rebuild a set of '83 carbs some years back. I pulled out a seal again today just to confirm and to offer pics as well for pinholenz and others who've not ventured into the seals yet. They have the same single inner lip with an outer edge that flairs and finishes in a taper. They're the same on my TDM CV's and lots of other carbs with an 8mm shaft and a 11.5 housing well. They are the same ones VB refers to #5599 on this page http://www.motorcyclecarbs.com/Throttle_Shaft_Seals_C680.cfm One can choose the more seal edge options offered, but I don't think it will be an improvement over the stock ones which work just fine.

I did find motorcycle carbs prices rather high for all their parts and did not use them. I also ran into the same 100 lot screw option and found a work around with Ace for a couple of bucks. I thought it great to have an allen head for future removal and with the flat top that is flush with the shaft it would be more streamlined ;D then the oval head. They have the same tapered bottom just like the stock ones. The 3 x 8 size sounds correct too.

Also, I'll add that for my TDM carbs did not leak at idle when performing the squirt test. But they were a bugger to get the needles to behave equally at idle and off idle. I then scratched my head and gave a squirt with the carbs just off idle and low and behold the left one sucked it in on the outboard side. With the new seals in the sync went as usual and performed equally at idle and off idle. The old ones were toast - truly toasted and brittle. Similar condition for the '83 Vee set.

Hope this all helps guys,
Rich

Some pics for reference of the easiest of the four seals to access on the carbs. Sorry they're not any sharper.

Pop the clip to gain access. 
(http://advrich.smugmug.com/photos/i-PMC8998/0/L/i-PMC8998-L.jpg) (http://advrich.smugmug.com/Other/Vehicle-Pics/15610468_5mWTBw#!i=2383979625&k=PMC8998&lb=1&s=A)

Remove the plastic washer and there's the seal.
(http://advrich.smugmug.com/photos/i-qCKgJ3q/0/L/i-qCKgJ3q-L.jpg) (http://advrich.smugmug.com/Other/Vehicle-Pics/15610468_5mWTBw#!i=2383981262&k=qCKgJ3q&lb=1&s=A)

Use a fine bladed flat screwdriver (computer/electricians) or dental tool to grab an edge and gently work it out. If they are really dry, you may just be able to pop the assembly against your cupped hand and it will fall out.
(http://advrich.smugmug.com/photos/i-VsFnP9q/0/L/i-VsFnP9q-L.jpg) (http://advrich.smugmug.com/Other/Vehicle-Pics/15610468_5mWTBw#!i=2383981938&k=VsFnP9q&lb=1&s=A)

The seal and stock screw. The outer edge in the pic makes the seal appear to have a lip, when in reality it is the light shining on the outward flaring taper of the seal. Sorry, I couldn't find a pic of the flat top allens I used.
(http://advrich.smugmug.com/photos/i-hcGvjn6/0/L/i-hcGvjn6-L.jpg) (http://advrich.smugmug.com/Other/Vehicle-Pics/15610468_5mWTBw#!i=2383983961&k=hcGvjn6&lb=1&s=A)

If one were to remove the C clip and the flat washer and then pack the area behind the flat washer with very heavy grease,  would one aquire a vacume proof seal in this area?  If so, reinstallation of the flat washer and the C clip might provide a viable alternative to seal replacment.

Quote from: QBS on February 26, 2013, 08:15:45 PM
If one were to remove the C clip and the flat washer and then pack the area behind the flat washer with very heavy grease,  would one aquire a vacume proof seal in this area?  If so, reinstallation of the flat washer and the C clip might provide a viable alternative to seal replacment.

If this seems a viable method then by all means. It will save you $3 to $5 in parts.

Will you do the same for the other three seals as well?

AdvRich, from your pics and post it would appear that it's possible to remove the seal without disturbing the butterfly valve.  Is this so?

You guys are convincing me to do this "if" I ever need to pull the carbs again.  But I am going to practice on some old 82 carbs before I touch the butterfly screws in my precious 83's

The screws retaining the throttle plates must be removed so the plates can be carefully extracted to allow the shaft to be pulled all the way out allowing seal replacement on both ends.  There is a certain amount of "finesse" involved in removing and installing each plate from it's respective bore.  Slow and easy is the name of the game here.  Because of the close tolerance fit, the plate may want to jam or cock in the bore. * DO NOT force or apply extreme pressure.  If it jams, reverse pressure to carefully free up and try again.  Properly aligned, the plate will slide through the throttle shaft cut out and the carb bore.  * Note the orientation of the plate after sliding out - There is a "top" and "bottom." Looking closely at the plate edge, you will notice it is chamfered in one direction to allow it to fit correctly when the linkage return spring brings the throttle plates closed.  Get it wrong and the butterfly plates will never fully close.

*important!!

Quote from: pullshocks on February 27, 2013, 12:27:15 AM
You guys are convincing me to do this "if" I ever need to pull the carbs again.  But I am going to practice on some old 82 carbs before I touch the butterfly screws in my precious 83's

Great! Good you have a spare set to work with.

+1

Quote from: vintage bikeworks on February 27, 2013, 01:30:28 AM
The screws retaining the throttle plates must be removed so the plates can be carefully extracted to allow the shaft to be pulled all the way out allowing seal replacement on both ends.  There is a certain amount of "finesse" involved in removing and installing each plate from it's respective bore.  Slow and easy is the name of the game here.  Because of the close tolerance fit, the plate may want to jam or cock in the bore. * DO NOT force or apply extreme pressure.  If it jams, reverse pressure to carefully free up and try again.  Properly aligned, the plate will slide through the throttle shaft cut out and the carb bore.  * Note the orientation of the plate after sliding out - There is a "top" and "bottom." Looking closely at the plate edge, you will notice it is chamfered in one direction to allow it to fit correctly when the linkage return spring brings the throttle plates closed.  Get it wrong and the butterfly plates will never fully close.

*important!!

Quote from: QBS on February 26, 2013, 11:36:04 PM
AdvRich, from your pics and post it would appear that it's possible to remove the seal without disturbing the butterfly valve.  Is this so?

Yes. I chose that easiest of seals to remove to provide a quick access for those that have not seen a throttle shaft seal, the well, shaft, etc up close.

QuoteSome pics for reference of the easiest of the four seals to access on the carbs.

The next easiest is the nutted one on the other carb.
The final two seals require the shafts to be removed as the throttle linkage plates are attached to the end of the throttle shafts. With carbs in hand it becomes very evident the level of work required for each seal to be accessed.

Hope this helps,
Rich 

I practiced on an 82 and found that the screws removed more easily when I backed them out just enough to cause the peened end of the screw to begin to bend up slightly which occurs as the screw becomes harder to remove, re-tighten the screw and cut off the end. I used a pair of hobbyist side cutters and they came out easily.    BDC

Again, great information here.  :)

Rich, thanks for the additional info and pics and really good tip to try the carb spray/vacuum test at different throttle positions besides idle. Higher flow or just having the shaft loaded differently might reveal what would otherwise go undiscovered at idle.  :(

To add to vintage bikeworks tutorial... I've only done one set so can't say if this is typical but my throttle shafts wouldn't slide easily from the carb body. They'd move so far and stop. I found the area around the threaded holes was ever so slightly deformed and needed to be dressed in order to have them come out without gouging the carb body. I carefully went over the affected areas with a dremel until they slid out easily. I don't recall now if it was at the staked side or the screw head side but if some resistance is offered in extracting the shaft look at those areas carefully. ;)

QBS, personally I don't have much confidence in grease being a good solution but let us know how it works. You'd still need to remove the screws to get grease behind the plate on the one side. If you've gone that far you might as well put the proper seals in, yes?

I probably had leaking shaft seals... but compensated the lean surge at 5k rpm by increasing the main jet sizes...

the nice thing about these downdraft carbs is... if you're leaking a little air in.. just add a little more gas  ;)

Rik, I was trying to avoid what is apparently unavoidable, namely going through the stress of removing the staked butterfly screws.

I think this is one of those tasks that have been made into a huge ordeal but in reality it's not that bad. The notion of doing it is more intimidating than the actual work. Take it a step at a time, be slow, cautious and carefull and it will be ok.  ;)

Sorry but to me , removing butterfly screws is night mare I experimented with it at work in 2002-2004  . The only way to get the screws out was to dremel the tips off , so they could be backed out . I could not come up with a way to support the shaft  and ended up bending s few, making them useless. Then I had  to find appropriate screws to replace then , as they are a one time shot. I tried O rings, but these caused the shaft not to return freely. i found on some carbs , like those on the XS650 , I could replace the one on the dead end of the shaft fairly easily.The other end was a different story.  Proceed with caution!

Sorry to hear you had so much trouble.  :(  Is there anyone else that found it difficult getting the screws out?  If so, any advice?

I didn't find the staking too bothersome so maybe it was the factory loctite? I know heat is recommended to loosen loctite so maybe one of those small "pen" butane torches would help? Plus it would add some fun drama if the fuel hadn't been completely drained!  :P

After 30 years, they have to be replaced ... if you want your Vision to run right!!! There is no substitute for good maintenance...

                         

as i said "proceed with caution"!

Ok, so while reading this thread I have two sets of '82 carbs sitting next to me in disassembled condition. I have managed to take all of the butterfly screws out (easily) ....BUT ONE!!! I went about it as carefully as I could but the philips head appears to be rounding out and I can't get a grip on it.

Bear in mind that the troublesome screw is in a set of carbs that came from a running bike that has relatively few problems. Should I proceed and find a way to get this screw out, or should I leave it and not bother? (maybe pack the seal with grease?)

The other carbs are getting new seals. The scews came out flawlessly, as did the shafts.

Quote from: munkyfistfight on March 04, 2013, 12:07:12 AM
Ok, so while reading this thread I have two sets of '82 carbs sitting next to me in disassembled condition. I have managed to take all of the butterfly screws out (easily) ....BUT ONE!!! I went about it as carefully as I could but the philips head appears to be rounding out and I can't get a grip on it.

Bear in mind that the troublesome screw is in a set of carbs that came from a running bike that has relatively few problems. Should I proceed and find a way to get this screw out, or should I leave it and not bother? (maybe pack the seal with grease?)

The other carbs are getting new seals. The scews came out flawlessly, as did the shafts.

Have you tried using Permatex valve grinding compound on the screw head to keep the screwdriver from slipping and/or rounding the head out?  (actually best used before the head starts to round out) This stuff should be available at any automotive parts store.  Permatex p/n: 34B

That's a good tip and I would also suggest heat to soften the factory thread locker. If the carbs are dry you can use a hobby sized torch available most hardware stores, Harbor Freight,  etc.  Another possibility is a soldering iron tip help on the screw. If that screw had been staked more aggressively than most you may need to get after it with a Dremel. Good luck and let us know how you make out.  :)

One important facet of seal replacement is getting the  butterfly back in, so that it seats properly .

I bought a "damaged screw extractor" set today. It pulled that baby out with no problems. So now that I have 2 sets of 82 carburetors apart, I'll want to replace the screws and the seals. I noticed on the AKVision carbs that one of the carbs had extra washers and a rubber o-ring outside of the seal. I'm guessing this could attribute to my hunting idle problems while tuning.

Very possibly  ;) Sounds like they may have been leaking and an attempt was made to seal it with O-rings. Unless they are a snug fit in the carb body and on the shaft OD I can't see them doing much.  :'(

I got my seals in from Boats.net yesterday. They look good. I have to finish cleaning the carbs and get the gaskets back and we'll be good to go. Let's hope these last another 30 years.  ;D

Hey maybe I missed something here guys, but are the throttle shaft seals listed above the correct part for both the '82 carbs and the '83's?   (Yamaha part # 256-14997-00-00) I'm gonna take on this challenge with my late model '82.

Yes, my understanding is both years use the same seal.

Those seals fit quite a few old Yamahas!

Definitely glad I have a "practice" carb.  One screw came out easily.  The other is going to require some Dremel work and a screw extractor.  I couldn't believe how little pressure it took to bugger the phillips slots.

Quote from: Rick G on March 04, 2013, 04:15:35 PM
One important facet of seal replacement is getting the  butterfly back in, so that it seats properly .

I've always left the butterfly slightly loose, and then closed the throttle several times to "seat" it before tightening them down. Is this how you do it, Rick?

On setups with multiple carbs, I also compare the crack of light around the edge (if any) between the different carbs. Be careful not to be fooled by sync/balance screw settings, if the carb is assembled enough for that to matter at this point.

Yes , basically that's it. But it takes several  tries  to get them seated correctly and it needs to be done quickly  befor the lock tite starts to set up.

Well I had the carbs out to adjust the float levels, so I bit the bullet and swapped out the throttle shaft seals too.   The posts above described the process very well.  Thank to  all who posted, and a special thank you to Vintage Bikeworks for supplying the replacement screws.  I would say it took about 2 hours, including trimming the screws to length.

The seals were very loose on the shafts.  I was never able to find leakage, but there is no way they were sealing.

After the switch I had to re-synch about 1/4 to 1/2 turn on the synch adjuster.

The carbs still go out of synch as RPM increases

Excellent! How is is running now? I noticed mine too were very loose in the carb and on the shaft but could only get the idle to fluctuate with carb spray sometimes and more often just after a ride when everything was hot. I can't imagine they seal well when they are so loose and have to assume that under load at higher RPM's the effect may be more apparent than at idle when you are looking for leaks.

Quote from: pullshocks on July 12, 2013, 09:05:46 PM
The carbs still go out of synch as RPM increases

That's normal so long as it's within reason. Just make sure they are equal at idle speed with the engine at operating temp and the mixtures adjusted properly.  :)

Actually sync is NOT done at idle , but at 2500 rpm. More accurate that way.

Rick I'm sure you have your reasons for doing so but to anyone else I'd recommend sync to be set at idle speed.

Old school twins and triples with split cable systems may benefit from Ricks procedure to ensure all the slack has been removed from multiple cables. Anything with unified mechanical linkage that lifts slides or opens butterflies should be synced at idle.  :)

All bikes should be synqed  at iaround 2500,you don't ride the bike at idle . 2500 is closer to where you do ride it.. As a long time mechanic  , rather than a modern parts exchanger . i learned this from another old timer . who is still active in his own shop at 76 years old.

The old timer that taught you came from an old time with split cables that aren't used on this bike.  :( All multi cylinder engine manifold pressures will differ slightly at different RPM's. How did your mentor come to accept the arbitrary 2500 number? Using your theory, why settle for 2500? Who rides at 2500 all the time - why not sync them at 5000, 3875, 6104 or redline for that matter?  ???  :o  ;D

The purpose of syncing the carbs is to ensure the throttles open at the same time. The point of opening is from the resting position which is idle. This is the critical point that has multi carb engines idle smooth and accept throttle with the least amount of fuss. And to be honest that smooth idle is really what it's all about - especially when talking about your particular nemesis the inline four.  :) This is what I learned at school where the instructors were old timers who prided themselves on not being parts replacers and who kept up with technology.  ;)

There may be applications where setting them at 2500 works great but I don't think this is one of them. So.... I guess we can agree to disagree then!?  :)

Sorry G, but I'm with Rick on this one. I've heard this as well, and it makes sense in my head.

The bike would definitely be easier to start when sunk at idle, but at operating RPM's when the engine is under load and when you're actually riding it would be more critical. I bet the difference between sync at idle and sync at speed are closer to each other than most decently running bikes are to either of these settings before being checked.


Any old school tricks for adjusting sync by ear, or is it truly a gauge only adjustment? (I own a real set of the gauges, I'm just curious because I remember fighting with it a lot before then)

OK this is just my own idle (pun intended) speculation...

The carb sync is designed not so much to ensure the throttles open at the same time, as it is to equalize the AFR between the cylinders.  If it was just for opening, then it wouldn't need adjusting over time, Right?

Since the carbs use different circuits between low idle and 2500 AND since you can't change the AFR at higher RPMs (without changing jetting / float levels) it makes sense to me to sync at 2500 using the sync rod, and then use idle mixture adjustment to sync at idle.

Is that sensible or am I missing the point?

  OK heres an idea, maybe if you put up at 2500 and  sync. it, then drop it to 1500 and see what you have.  The amount of the throtle plate would be open at 2500 is still very small.

Sorry but the purpose of syncing carbs is NOT to insure they open at the same time, but to insure that they pull evenly under load.  You may rest assured that  the skills acquired over a life time of working on motor cycle engine Will not become obsolete!  In fact new skills are  built on the basis of older acquired skills.

QuoteSorry G, but I'm with Rick on this one. I've heard this as well, and it makes sense in my head.

No problem Jim, you owe me no loyalties and I'm not afraid to stand alone in the right  :P But seriously, what is it specifically that makes sense to you? No answer from Rick so I'll ask you: why 2500 rather than any other RPM?

QuoteThe carb sync is designed not so much to ensure the throttles open at the same time, as it is to equalize the AFR between the cylinders.  If it was just for opening, then it wouldn't need adjusting over time, Right?

Sort of.  :) You are right - it's more than just the opening as that would not change substantially over time other than through wear of the linkage. "Throttles open the same amount" and "vacuum readings the same" are used interchangeably even in technical articles and manuals although they are not necessarily the same thing. In a perfect world they would be. Since it's not a perfect world, we measure and adjust manifold pressure to be equal by moving the two plates relative to each other. Over time this changes and periodically needs to be checked.

The reason sync (vacuum) changes over time is manufacturing variability and wear of the sealing surfaces i.e. piston, rings, cylinder wall, valve seat and face. These things are not the same (between cylinders) when the engine is new and vary more as the engine wears.  Within the realm of the engines serviceable life, adjust for equal vacuum and the plates will be reasonably close. If you were racing you might ignore all this and just ensure the plates were fully open when the linkage is at WFO. Some early forms of race specific carbs didn't even have much of an idle circuit. I however ride on the street in the real world and the Vision is no race bike!  ;D 

A few things to consider....  Equal vacuum readings doesn't guarantee an equal AFR or a smooth idle as in the case of obstructed jets on one carb. You can adjust the sync to achieve equal readings between the 2 cylinders but it still idles rough. Carb synchronization won't clean a dirty carb.  :( You can have one cylinder with a leaking rubber manifold and still adjust the linkage to get the vacuum readings more or less equal. The throttle plates will be way out and the engine will idle rough because a carb sync wont plug vacuum leaks.  :(  There are other scenarios but you get the point. Everything else has to be to spec before you can sync the carbs. A good carb sync won't cure other non related problems.  :)

and finally....

QuoteYou may rest assured that  the skills acquired over a life time of working on motor cycle engine Will not become obsolete!  In fact new skills are  built on the basis of older acquired skills.

I agree.  :)

There are several reasons to sync the carbs and one is to have the throttles open the same amount (vacuum readings the same if you prefer) at idle, to ensure they open in unison, and yes even so the engine pulls under load. Here's the key point - they can be off slightly and you'll never notice it under load. If you think you can notice it under load, you still can't. You are noticing some other engine deficiency or you simply want to believe you can notice it.

Where you will notice it is at idle. Call it a conspiracy if you wish. The factory wishes their product to run smoothly at idle - it makes for happy customers. Is this at the expense of performance elsewhere in the rev range? Absolutely not. Not for street riding in the real world anyway.

If your engine is in good health and the carbs are synchronized at idle, the rest of the rev range will take care of itself. How can it not? The throttles are in sync. Yes, vacuum readings will vary between cylinders at different RPMs. This is normal (within reason) and unavoidable. So if you wish to choose an alternate RPM to set them at for your sake I hope just by chance it also means they're balanced at idle. If not you gained nothing and lost a smooth idle.

Now this is important....If you sync the carbs at idle with good equipment and technique and notice any of the following:

-rough idle
-surging at steady cruise
-a miss at high RPM
-a stumble off idle or any other RPM for that matter
-poor fuel economy
-lack of power
-erratic popping under decal
-sputtering, coughing, wheezing, or any other flu-like symptoms  ;)
-or any other performance woe

it is not the fault of the carb sync. There is something else (or several things) wrong with your bike.  :(

Many people tend to over dramatize the significance of the mysterious carb sync procedure and blame it for things it can not possibly effect. At it's core, it's main function is to ensure a smooth idle. That's it. Everything else just falls into place as a result.

Thank you Rik.  Total agreement. Excellent and through explanation.  Wonderful for those of us that began our travels in the world of fuel injection, never having interfaced with comparativley archaic carb technology, and all its hidden details and secret handshakes.

I have posted a chapter from the Vision carb tutorial that I have been working on. I'd appreciate comments and suggestions -especially if my terminology becomes confusing or if I am plain wrong!!

This first part deals with replacing the throttle shaft seals.  and is posted over on the general forum.


http://vimeo.com/70672209         (with music)

http://vimeo.com/70668221

Quote from: Rikugun on July 19, 2013, 08:12:52 AM
Now this is important....If you sync the carbs at idle with good equipment and technique and notice any of the following:

-rough idle
-surging at steady cruise
-a miss at high RPM
-a stumble off idle or any other RPM for that matter
-poor fuel economy
-lack of power
-erratic popping under decal
-sputtering, coughing, wheezing, or any other flu-like symptoms  ;)
-or any other performance woe

it is not the fault of the carb sync. There is something else (or several things) wrong with your bike.  :(

This is most disconcerting! When I adjust my carbs so they're synced according to the gauge, I have any of these symptoms that are listed...sometimes all of them! I've gotta get into that top end...

Quote from: pinholenz on July 20, 2013, 12:00:50 AM
I have posted a chapter from the Vision carb tutorial that I have been working on. I'd appreciate comments and suggestions -especially if my terminology becomes confusing or if I am plain wrong!!

This first part deals with replacing the throttle shaft seals.  and is posted over on the general forum.


http://vimeo.com/70672209         (with music)

http://vimeo.com/70668221

A most excellent video tutorial John. 
I'm sure that will help a lot of people.  More would be very welcome I'm sure

I agree, very good tutorial!  :) I'm sure the video length belies the actual time invested in it's creation so thank you. I liked the use of a second set of screws to set and hold the plates prior to application of threadlocker. Not sure if that's your idea or someone else but a good tip.


Roro, you brought up a good point relative to throttle plate position vs. vacuum readings. I commented on this but it may have gotten missed due to the page break. I edited my comments in an effort to be more clear - hopefully it is?

And on the topic of the carb sync, I should apologize for my part in the hijacking of the thread. :-[ It's a worthwhile discussion but should have been made it's own topic.

Thanks for the reply I did miss it due to the page break - I really love how RoV has developed lately.  Less proselytising, a lot more thought, and consideration of ideas.

My carbs are squeaky clean, with new jets and tested for leaks.  Even so, there's a noticeable sync difference between low idle and 3000 RPM.   I assume because the 122.5 / 127.5 jetting was suitable for a new bike with stock air filter, and stock exhaust - none of which apply to my bike.

I've been tuning mixtures to highest vacuum (at lowest possible idle) rather than highest RPM since I got my proper manometer.  It's easier to see the smaller changes, and quicker since you do it on a per carb basis.

Just for the record....

I would like to go on record to state that throttle sync is primarily all about balancing the load during acceleration between cylinders exactly as Rick G and a few people that know what they are talking about have said, and it didn't take more than one sentence to say it.  You really want to check to see that that vacuum draw is as even as possible at various rpms.  2500 is a good spot to check it at.  Idle is set with the mixture screw and can be fine tuned after the sync is checked. They do affect each other, so you get your idle decent, (idle screw backed out as much as possible to prevent holding throttle plates open) then sync checking for even vacuum pull at load rpms (holding it steady for check), and then come back to fine tune the idle with mixture screws.

Thank you for your opinion Cecil.

Its NOT just Cecil's opinion, its a fact !!

Quote from: Rick G on August 03, 2013, 04:52:36 AM
Its NOT just Cecil's opinion, its a fact !!

That was dogmatic.
This argument is on every bike forum in the world.  Surely there is more than one way to tune a bike.

I concede there are several generally accepted methods of syncing carbs. To suggest there is only one way would be arrogant. Having said that, it has been my experience that the Japanese manufacturers' intent is to have carb balancing done at idle. I should also like to limit this observation to street prepped, minimally modified, multi-carb engines with mechanically linked throttles and unified idle speed adjustment screws. Like the Vision for instance.  :D

I have made a real effort to be more open to differing ideas - admittedly the older I get the more difficult this becomes..... :)  However, anyone who has read my contributions to the site knows I have no problem questioning convention when I see a reason to. I also realize "standards" often become standards for good reason. With that in mind, I invite the "2500 camp" to change my mind. Convince me and be persuasive.  :) Certainly there is some good evidence out there you can point to that demonstrates one way to be superior over to another.

BTW, I do not recognize the opinion of forum members (myself included) as expert. I'm going to need documentation from reliable known and peer reviewed/accepted technical sources. Factory service manuals would be acceptable for instance. Which brings me to another interesting point no one has brought up yet. Unless I missed it somewhere I don't see in the Yamaha Vision service manual that it specifies a speed to balance the carbs at. I'm curious to learn forum members' thoughts on why that may be.

The point that I am making here disagrees with your statement Rikugun as you said,

"At it's core, it's main function is to ensure a smooth idle. That's it. Everything else just falls into place as a result."

My point is that you can easily adjust a smooth idle with the mixture screw (make it run perfectly at idle) and have it run like a bucket of junk without a proper synchronization.  The synchro is used to get the carbs into synchronization for running under load. In order to check synchronization you have to open the throttle plates and that necessarily takes you out of the idle circuit.  That is the phase above idle where it greatly affects engine performance and you can feel the difference, especially in multi-cylinder machines.

A mechanic generally uses carb synchronization to confirm many things about the engine performance.  It is a check of general engine wear, engine faults (air leaks, etc.) that may affect performance dramatically all under "load" conditions.  Generally you start the synchro above the normal idle circuit anyway and after setting the idle  (a slightly fast idle by adjusting the carb stop) to do a proper comparison of what is happening under load.  At this point you are out of the idle circuit and into the pilot jet circuit, then at (? rpm) the main jet kicks in.  Now, if you have a jet blockage you will notice a drop in vacuum pull in the rpm of either the pilot or main jet and this can show up in the synchronization if you do more than just check it at idle which is really not a proper synchro at all.  As I said, a smooth idle is set with the mixture screws not the synchro and that is a scientific fact, and normally common sense because of carburetor design.

So your theory of this only being important to set the idle is just plain wrong.  I wish to be politely clear here, it is not my purpose to convince anyone who knows everything, but to enlighten those who need or want the help, so hopefully this helps someone.  This post is for those who want to listen not those who already have their minds made up, so feel free to ignore it if it doesn't suit your fancy.  BTW if you find a shop manual that tells you everything about tuning an engine let me know, I want a copy.

And, (from my limited experience), you need to get the carb sync vacuum right at idle first, simultaneously juggling the mixture screws to get a smooth idle. Adjust one and it affects the other. I guess that is why the mixtures screws were capped off after setting at the factory.

So if I understand Cdnlouie right, unbalanced sync vacuums at  RPMs higher than say, 1300, signal that there is else something adrift in the system - such as restricted airflow, partially blocked jet, valve clearance problems, leaking YICS,  (restricted exhaust?)  and so on. That makes more sense than trying to re-sync the carbs at different RPMs and having to choose one setting in preference to another.

However, surely you HAVE to have the butterfly valves in sync at idle AND the mixture screws nicely adjusted in order to get a smooth idle?

I love this forum.  :)

Absolutely Pinholenz, the idle circuit is a component of balancing that starts with the mixture screws and the throttle plates closed.  The next aspect includes the rest of the throttle range where (depending on the linkage used with the type of motorcycle) you synchronize the lifts of each carburetor so they all pull evenly throughout the rpms.  Things like vacuum flutter will perhaps indicate a leaking valve or some other engine condition that you may want to look into if they don't pull evenly.  That's why this action must only be performed after checking valves and other tune-up items so that you know that all those aspects are covered and you can do a general performance check to see your motorcycle is in good condition. In the eighties when the Vision first came out Yamaha also introduced the use of an exhaust gas analyzer that was to be used to get the mixtures set properly first and then the synchronization would check the throttle opening as the plates began to lift. That first off-idle zone, say 1000-2500 is where you are watching to see that you get even pull and that is more important (or perhaps indicative) than the idle zone which be a bit off because of more fluctuation in vacuum at this point.   

Good luck with the factory manuals , there full of errors and don't alway agree with each other.
My "opinion " come from working with people who  were in the trade when the Japanese invasion started and the accumulated knowledge   was  better than any manual.

Quote from: Cdnlouie on August 02, 2013, 06:40:58 PM
Just for the record....I would like to go on record to state that throttle sync is primarily all about balancing the load during acceleration between cylinders exactly as Rick G and a few people that know what they are talking about have said, and it didn't take more than one sentence to say it. 

So Cecil, Rick and a few others know what they are taking about and the rest of us are just a bunch of schlubs. Good to know and believe me, we appreciate hearing it! Also, apparently one sentence wasn't sufficient after all! Good for you!  ;)

Quote from: Cdnlouie on August 04, 2013, 12:01:08 AM
I wish to be politely clear here, it is not my purpose to convince anyone who knows everything, but to enlighten those who need or want the help, so hopefully this helps someone.  This post is for those who want to listen not those who already have their minds made up. 

Having been at the receiving end of your snarky comments in the past I'm guessing this is aimed at me? The irony is you could also be describing yourself! Much like me you are a bit of a know-it-all and don't like being wrong.  :P Interesting, huh?  And BTW, starting a sentence with "I wish to be polite"... doesn't absolve you of whatever comes out of your mouth next.   ::)  ;)  I honestly won't take offense to your comments so just say it and own it. We're all big boys here. Fair enough? Good.

Quote from: Cdnlouie on August 04, 2013, 12:01:08 AM
BTW if you find a shop manual that tells you everything about tuning an engine let me know, I want a copy.

Gosh, I sure haven't but will let you know if I do.

I guess this is in reference to my query regarding Japanese factory shop manuals and the 2500 RPM sync? If so, my question remains unanswered. It is a serious question and I'd like to know.  Certainly someone must have a service manual to a Honda Kawasaki Suzuki or Yamaha multi cylinder bike laying around? If anyone has a reference to this they can share I sincerely hope you will.  I've looked in the few manuals I have and they say idle - except for the Vision manual which doesn't indicate a specific RPM. On that note, I'd still like to learn others opinions of why engine speed during synchronization is not mentioned in the Vision manual. This is not a test or trick question but rather a genuine interest in learning others ideas on the matter. 

I sense that Rick and Cecil don't regard factory service manuals as an authoritative and reliable source of technical info. I do (with certain stipulations) so humor me. We can argue how accurate a factory manual is but if we see references to 2500 RPM sync over and over from several makes and models, I'd think some amount of credence can be given to the claim. If this is the preferred method I certainly want to know. And if only for certain models, why just them.

This post has got me thinking about all this again - timely as I'm in the middle of rebuild v3.0.

Despite how I've done it in the past, when I think about it, syncing at idle makes no sense.  The butterflies are closed.  They are supposed to be closed.  If you need to open one of them a crack (which is what you are doing if you deploy the sync mechanism) then you really need to take another look at your mixture settings.  Since most people seem to use the fairly crude "midpoint between stumbles" technique there's a good chance that their mixture settings are sub-optimal.

Jetting is a coarse adjustment - the implication being that you can't fine tune the jets to be balanced between cylinders unless you also employ the sync mechanism. 

Idle mixtures on the other hand are an infinitely fine adjustment, if one cylinder is slightly stronger at a given sync setting, you can easily back that one off to achieve balance.  I think you can get away with a less than optimised burn (maximum power) at idle - it's not like you are going anywhere but it will need to be balanced for smooth transition.  Again - this can be done with the mixture screws. 

My plan then is to adjust mixtures using max vacuum and EGA, sync at a higher RPM, and then go back and readjust idle mixtures to have balanced vacuum.  Repeat until perfect.  The result should be balance across the entire RPM range, and optimal power while the bike is going, rather than when it's idling.  Can anyone see a flaw in this plan?

PS I also wonder if High RPM syncing not being recommended is not so much that it's undesirable, but more due to the dangers of potentially sucking mercury through the engine.  Not an issue with my metal stick manometer :-)

Oh not you too!!   :D  :D You're over thinking this my friend...

Probably - I tend to do that.
Actually I don't care to much as long as it goes well.  I'll try both ways and stick with the one I like the best
It's only a 1/2 hour job

No , Rikugun , not every one else , just you !

Looking forward to your results Roro.  If you wouldn't mind noting down your EGA readings, that would be most interesting.

Also, will your engine idle with both throttle plates completely closed?(I.e. idle knob completely backed off and sync rod disconnected? ) If yes, what RPM?

  um Guys, I am going to have to ask everyone to tone down the personal comments.
  let's keep this amicable.
  we don't have to agree 100% on each and every minute detail.
  carburetors are your friends...

  that is all.
 
   --Admin

Admin - PM sent.

QuoteNot an issue with my metal stick manometer :-)

How does this work? Is this store bought or something anyone can make at home?

QuoteI'll try both ways and stick with the one I like the best  It's only a 1/2 hour job

That seems like a very reasonable course of action.  :)

Regarding your proposed balancing regimen using EGA to optimize mixture settings, does the process start with the assumption the plates are more or less even or is that not critical initially?

I bought one of the real Motion Pro sync sticks a year ago, and it blows my homemade sync tool away. If you can swing the cash, I definitely recommend buying the real tool!

If you're friends with a service shop, usually they're happy to let you use theirs for a couple of beers :)

I use a morgan carbtune - imported from the UK.  http://www.carbtune.com/ (http://www.carbtune.com/)  Metal sticks so it is safe as can be for both bike and environment.  I've done a dozen bikes with it - it's more than paid for itself in beer :-)

Starting sync will be damn near spot on anyway as the bike was running before disassembly and carbs recently overhauled. 

The EGA is a commercial 4 Gas -  I can post readings but they won't be very interesting.  I'd love to be able to take readings at WOT, but that would be tricky - it weighs about 40kg and is mains powered.  I've heard of people doing it on the main stand with the rear brake on.  Sounds crazy dangerous to me.

I use a 4 vacuum gage manifold , bought it 12 years ago . it does a fine job. I disliked the mercury tubes.

I like that Morgan Carbtune. It looks like it doesn't have the "air bubbles" flaw my Hg type does. My brother's birthday is coming up so might be a good gift idea. I'm sure he won't mind if I borrow it so it serves double duty.  ;D

A great gift idea.  It's my tool I like the most and the only one I wouldn't replace with something better if Pippa Middleton fell in love with me and gave me all her money to spend on tools.
Shipping from the UK can take ages, last parcel took 22 days for 7-10 day service.  so leave plenty of time

Must have come by ship?

Quote from: roro on August 09, 2013, 11:28:22 PM
A great gift idea.  It's my tool I like the most and the only one I wouldn't replace with something better if Pippa Middleton fell in love with me and gave me all her money to spend on tools.
Shipping from the UK can take ages, last parcel took 22 days for 7-10 day service.  so leave plenty of time

Theres only one tool I would need if Pippa fell for me... :P

Wow, this debate on carb sync procedure is quite a controversy. Being just a little crazy, I'll stick my two cents into it. My experience as a dealership motorcycle mechanic in the '70s and attending Honda technical training school ("factory trained") in those days is this: the multis were synced with a four vacuum gage set (the factory tool) at idle.

I also just checked three factory manuals from my bookshelf, a Honda CB/CL 450, a Honda CL 72, and a Kawasaki KZ 400. All specify carb sync at idle, the Kawi running with vacuum gages, the older Hondas not running with throttle movement synced through feel and cable adjustment. The Brit bikes I worked on before switching to Hondas were synced like the older Honda twins - engine off, air cleaners off, fingers in the carbs to feel the throttle slides as they moved slightly up from their fully closed positions. With a carefull ear, that could also be done by listening to the slides click as they hit their stops when the throttle grip was opened and closed and adjusting for one simultaneous click.

All of those had slide carbs. The vision has butterfly's and the carbs have no resemblance to the throttle valve carbs

I was there too,  started in 63 and  quit in 80.  Service manager  for Allied Suzuki in Upland CA. , Norwalk cycle (BMW and Yamaha and Mason motors  In Pasadena CA. Yamaha, Triumph  and Vespa. Went back to it in 2001 for Motorcycle specialties in Salem OR . and Dunton Motors in Kingman AZ . Arctic cat. from 2005 to 2007 In OR> I worked for  Randy Lane  , a nasty tempered old coot (older than me)  who was VERY sharp and taught me a lot. He was the one who started me syncing at 2500 rpm and he was right.

Hey welcome aboard Neil! Good background on the "old days" and exactly the procedure used to synchronize those old engines. The controversy here is really about "significance" of the carb synchronization.  There is a difference between synchronizing "for idle" and synchronizing "at idle." There is no doubt that you check the vacuum levels "at idle," but this is where the Vision is quite a bit different than the slide carburetors. The goal is to get the mixture screws dialed in so that you get a balanced idle setting, before you start fiddling with the throttle plates (assuming they are at least set close enough to close properly). Here is the tricky part, most of the Vision carburetors always include more turns out on the rear cylinder than the front.  On the old multi-fours with slides you never had to worry about the mixture screws except to set them all at 1.5 turns out and you were golden.  Just the same, using the vacuum gauges of the past you would not just set the synchronization without observing how the engine pulled, off the "at idle" position. That needle bounced like crazy at idle and you could only be sure you got it right by bringing it under load. Sure you do the adjustment "at idle," but you also observe the vacuum under load to see that they really are pulling together.

The Vision needs to be observed for vacuum alignment "at idle" (primarily a result of mixture settings "for idle"), then observed for behaviour when you transition to the low speed fuel circuit and finally the main jet circuit.  Any fluctuation in vacuum during these transitions may indicate where you have carburetor blockages, engine wear, or something else you can't see. I hope this sheds some light on the misperception that it is one or the other position to check synchronization, in reality it includes both.  A technician must decide the "significance" of his vacuum readings and end up making his final adjustment according to that evaluation. I believe that Rick is taking into account the bigger picture or "significance" of a carburetor synchronization (at least that is the way I understood it).

Thanks for the additional info, Louie.
The bouncing gage needles are not an issue with the Honda factory gage sets I have used and own. Each gage has a damper valve that can be adjusted to reduce the bouncing to very little - within 1 increment or less on the gage face. It is true that the mixture or air screws base setting was typically 1.5 turns out, but there was always a +/- part of the spec and we knew to fine tune them they should be turned in or out to find the highest idle speed. On the Vision carbs, I do know about the different starting point setting for the rear from the front. Perfect sync on the gages at idle is great, but how the motor pulls and responds to opening the throttles off idle is also important.

Maybe this controversy can be concluded with the suggestion of checking sync both at idle and at a higher RPM, see if it is different or not and adjust to individual preference.

BTW - another tidbit of factory info - my 1983 Canadian Yamaha RZ 350 has two cable operated carbs. Each carb body has a sight glass window in it and each throttle slide has a mark on it that aligns with the windows. The marks are visible in the windows when the slides are all the way up...full throttle. This is for carb syncing and the factory manual's instructions are to open the twist grip all the way and check the throttle slides' marks in those windows, and adjust the cables as needed to position the marks identically in the windows. So, this factory info is to sync at full throttle. My training was full throttle syncing is for racing and sync at idle or at a small throttle opening for street riding since that is where most riding is done.

Couldn't agree with you more! You have nicely described the different scenarios of carb synchronization including both purpose and design.

I also worked for a Honda dealership back in the 70's which also included the one of the oldest Brit bike dealers in Canada, those were exciting days with Honda leading the pack. Yes the vacuum flutter adjusters were a good idea for the time, but I sure enjoy the new Morgan Carbtune.  For the early 80's I moved to a Yamaha dealership and caught the wave of the next most exciting motorcycles in the era (Vision included).  However, I never owned a Vision until the start of the 21st Century (my second childhood).

 

Syncing at idle is a given. syncing again  at 2500 provides  much smother performance and better throttle response. For racing it , because the throttle will be wide open much of the time , is a given.
I have spent  onsiderable time with my fingers stuck in the carb throat of a Triumph or BSA  ( bastard stalled again)  (British scrap aluminum) or as the Qubecois  say it   Motorcycle often stopped .  I would put my finger on my left hand in the left carb on a Bonniville and observe the right one . The splayed ports on the Bonnie prevented seeing both at the same time . BSA's and jap bikes you could get your thumb in one and your index finger in the other  and feel when the were lifting. My 4 gage manifold with damping valves makes it so much easier!

"BSA's and jap bikes you could get your thumb in one and your index finger in the other  and feel when the were lifting."
Nortons, too.

Quote from: Neil on August 27, 2013, 12:08:12 AM
Being just a little crazy, I'll stick my two cents into it. My experience as a dealership motorcycle mechanic in the '70s and attending Honda technical training school ("factory trained") in those days is this: the multis were synced with a four vacuum gage set (the factory tool) at idle.

Thanks for you input Neil. This was my experience as well and no worries about being called crazy for voicing your opinion. I've been assured by the administrator of the site we promote an environment where all can feel safe voicing an opinion with no fear of reprisal.   :)

Quote from: Neil on August 27, 2013, 12:08:12 AM
I also just checked three factory manuals from my bookshelf, a Honda CB/CL 450, a Honda CL 72, and a Kawasaki KZ 400. All specify carb sync at idle, the Kawi running with vacuum gages, the older Hondas not, running with throttle movement synced through feel and cable adjustment. The Brit bikes I worked on ... were synced like the older Honda twins - engine off, air cleaners off, fingers in the carbs to feel the throttle slides as they moved slightly up from their fully closed positions. With a carefull ear, that could also be done by listening to the slides click as they hit their stops when the throttle grip was opened and closed and adjusting for one simultaneous click.

Thank you for looking up and sharing the info from the Honda and Kawasaki manuals which plays into this. There are key differences in the carbs on these bikes - split cables vs. integrated linkage - which dictate available sync options. The KZ manual outlines vacuum gages at idle because it is faster, more accurate and more importantly - it can be done.  Those carbs have mechanically linked throttle plates and idle speed adjustment as well as ports for connecting gages - just like the Vision. The Honda and RD twins referenced have split cables and separate idle speed screws. This is true of Yamaha TX carbs as well as most old British, Italian, German etc. makes as well. A very few of these (usually later versions) may have vacuum ports available making the sync procedure less dreadful as gages rather than less accurate visual/tactile methods can be employed.

There are as many ways to sync split cable systems as there are opinions on the matter. I won't address mixtures here but relative to sync, there are two concerns - the individual cable adjusters and individual idle speed screws. The first step is to tension both cables with the twist grip and adjust the slides to be the same. The Mikuni carbs with the dot on the slide used on some RD's and other models simplified this step. This ensures both slides lift simultaneously with throttle application and that they are open the same amount with tensioned cables but does not alter there resting (idle) position.  The next step is to sync the carbs at idle using the idle speed screws. Without this step, idle/off idle performance can suffer dramatically. This also plays into the ability to effectively make mixture adjustments but I promised not to go there...  :D  Again, there are numerous effective and no so effective methods. Most of these methods aren't practical or won't work on the Vision but are interesting from a historical reference point.

Relative to mechanically linked carbs in general and Vision carbs specifically, I've looked for evidence the 2500 RPM sync method offers some advantage and could not find anything other than anecdotal. Moreover, I can see potential problems with this method which make it less desirable to me.  This is  just my opinion and I will continue to use sync at idle as a given. Naturally anyone can disagree with me and I will support their right to do so 110%.   ;)

While I was chasing carb demons I put long hoses on my synch gauges and set it on top of my tank bag so I could watch the gauges under acceleration and deceleration. Other than being a very dangerous distraction, it did provide an amplified view of vacuum differences.
In general I found it to display and possibly clarify the variances I could see when setting the synch at idle. Slight differences, that were hard to distinguish with needles bobbleing at idle, became more exaggerated under load.
It helped answer questions like did I screw the damping adjustment on the gauges more on one than the other? and is the variance I am seeing within the tolerance of accuracy of the individual gauges?(the cheapo ones from Mike's XS).

I too used extra long hoses without any damping at all, even when they were imbalanced I didn't have to worry about sucking red transmission fluid into the cylinders. Once they were balanced I didn't see a lot of difference from one idle adjustment to another. I've only done my bike and the help available here made it go smoothly. Should be a simple matter to try both methods and see where your bike performs best.     BDC

The Honda's you mention have Constant velocity carbs , The Vision does not . There is really no comparison . Its apples and oranges.