The evil EPA and V drivability.

[QBS]

First off, #50 for main fuel is very wrong.  I pulled the main fuel from my '83s' front carb.  It reads 130.  I feel that, at least for my bike, that is a good size.  This data is not in line with data reported by roro for my bike.  However, with approx. 88k miles on it, it will still red line 5th gear.  This tells me that it's making good power, and in at least in the case of my bike, should be left alone.  Fundamental question: Does a bigger #jet equate to a bigger hole or visa versa?

I investigated the emulsion tube jets on a spare set of '83 carbs and found #180s in both units.

I feel that the jets that should be focused on are the primary, air, and emulsion tube in that order.  The emulsion tube jet may be ok as is, but I'm not sure.

What we need to determine is what is the functional relationship between the primary jet and the air jet.  If you mess with one, how does that effect the function of the other?

No doubt equally important, what is the effect of altering the size of the emulsion tube jet and or its' emulsion tube hole sizes and or number of them?  I vaguely remember, long ago and far away, a post from either an Aussie or Kiwi Vnary who had a lot interaction with Ducati aficionados.  He made a passing remark about altering the emulsion tubes on Ducati carbs for the better.  I think he said that he had done a similar mod to his V with positive results.  Hopefully he'll read this thread and speak up.  I really want to understand the Emulsion Tube Jet much better.  Until its' function is understood, no meaningful positive changes can be made.  My gut feeling is that the random midrange power loss that my bike and I suspect a lot of other Vs, experience at steady state cruise is related to this jet/tube.

Fiat-Doctor has made several comments regarding the similarities between our Mikuni carbs and Webers, and Weber related mods he has mad to our Mikunis'.  Webers are reported to be very tunable and, once well sorted, excellent and stable units.  The bike mag reviews back in the day made mention that V carbs were close copys of Webers'.

We need to determine what size our primary jets are.  This could be the starting point for V stumble elimination.

After reading the interaction between jasonm and Rikugun regarding leaky throttle shaft seals, it seems to me that such leaks would effect mixture a idle, but very little at larger throttle openings.  This is because so much additional air would be entering the carb, and thus lowering the vacuum, that the small shaft leak would go unnoticed by the carb.

Cheers guys.

[treedragon]

roro

if it's any use the  Engine number is 25R,  Frame is 25R-004113
Which model carb I have no idea really, just one of the later ones I guess. Just sorting out which jet is actually what is bad enough before I have even started looking.

Pics are on the air box mod post. The idea of the extended stacks was to speed downdraft velocity.

[Night Vision]

the #50 jet is the fuel pilot jet on an 83
82's have #60 fuel pilot jets..

the 82 has different sized mains (122.5/127.5 stock) because of the difference in exhaust pipe length...
83's have different diameter headpipes than the 82s so they run the same size mains front and back..

you'll see different combinations on the air jets... but mostly I've seen 130/135 with the vac flapper here on the board.

rejetting is not as hard as some have made it out to be.... bottom line is each carb will be different... find out what works for you... there is no one size fits all...... but I still stick by my suggestion to go bigger if you're stumblin or surging.  

[jasonm.]

Smaller ID...thus the exhuast gases actually flow better at low rpm, if not all rpm.  So there was no screwing with different air jets.  And mains also allowed to be the same.  Simply...they got in correct in the 2nd year US models.

[Rick G]

You may change jets until your blue in the face. Stumble is best eliminated by careful synchronization and adjusting  the flapper opening .

[Rikugun]

and adjusting  the flapper opening .

Rick, In what way - mechanical adjustments like bending linkage or flapper? Modify the vacuum control? Modifying the airbox opening? More details please.

[Lucky]

the mounts for the flapper door are slotted so moving the door is a fine tuning sort of adjustment.  i think the screws are in plastic so don't strip 'em

[Night Vision]

Could you clarify the 130/135 air jets you've seen on the board - is that just 82's? If so, much like with the mains, is that also due to exhaust length difference?

the parts fiche of the carbs on the yamaha site is for the 82 carb... the parts list shows 122.5/127.5 mains, #60 fuel pilots, and 130 air jets..

if you look at the flapper update instructions, http://www.ridersofvision.net/Technical/Airbox/airbox.html

they list a 135 air pilot for the rear.. they also list a 122.5 main for the front carb in the flapper kit...which contradicts the parts fiche? why intall a 122.5 front main if it was stock?


you'll find other discrepancies in the haynes manual too... hope that clears things up  ;D

[Lucky]

i think the differences come with different printing dates...  some of you may not know this, but the Yamaha workshop manual valve shim chart is wrong too...

[The Prophet of Doom]

Could you clarify the 130/135 air jets you've seen on the board - is that just 82's? If so, much like with the mains, is that also due to exhaust length difference?

the parts fiche of the carbs on the yamaha site is for the 82 carb... the parts list shows 122.5/127.5 mains, #60 fuel pilots, and 130 air jets..

if you look at the flapper update instructions, http://www.ridersofvision.net/Technical/Airbox/airbox.html

they list a 135 air pilot for the rear.. they also list a 122.5 main for the front carb in the flapper kit...which contradicts the parts fiche? why intall a 122.5 front main if it was stock?


you'll find other discrepancies in the haynes manual too... hope that clears things up  ;D

You are right NV , but do you know that all XZ's were shipped with a front 122.5 as per the parts fiche.  Fiches are revised often, expecially in the early period.

In the flapper modification instructions pg3 it states...

[note] For the front, pilot air jet is provided on the float chamber cover assembly.

That does not suggest a 130 Front to me.

[Night Vision]

In the flapper modification instructions pg3 it states...

[note] For the front, pilot air jet is provided on the float chamber cover assembly.

That does not suggest a 130 Front to me.

good catch? but I'm not sure  :-\

before I started molesting my Vision... she had plugged pilot screws, the flapper mod with the updated front carb top, and 130/135 air pilots.... I assumed this was the correct configuration and that a dealer must have installed the update because the previous owner was a poet... not a tinkerer... kicker is; I had a new front top in a box from a kit and scavenged the jet without paying attention to the size  :-[ ... at the time, I was just gathering jets from here and there for jetting games

[Night Vision]

You may change jets until your blue in the face. Stumble is best eliminated by careful synchronization and adjusting  the flapper opening .

Rick, I tried that... a few times, never worked for me.  Jason has his set so it is opened slightly while at low draw...

I think the stumble is caused by a sudden lean situation where the flapper opens too quickly.. my reasoning being is the two nickles trick that slows the opening on the non-vacc doors... that smoothed out lots a stumbles on non updated 82s

dirty/plugged jets will cause an extreme stumble... again a lean situation

[johnclemens]

Just a few of my thoughts.
I don't have my notes from racing a stock vision anymore. However I remember running stock jet sizes when I had a stock exhaust.  I would agree with Rick. You can mess around all you want with jets and not solve the stumble. I found a solution to stumble both on my racer and stock street bike. It was to retain all stock jets and adjust the Accelerator pump shaft. You can screw it in and out and that will give you more or less of a shot of fuel when you crack the throttle as well as affecting when the squirt happens I think.
I had access to a dyno during the time and we screwed with everything. Only to return to the original jets, Flapper and YICS. If you have any leaks in the YICS, or the hoses are pinching flat from suction.  You are spinning your wheels trying to get rid of stumbles. Also make sure your intake boots aren't cracked and everything is tight. You'll get nowhere fast if you have intake leaks.

Remember gas is crap now too, That doesn't help. I would stick with 92 octane.
Good luck.

[Rikugun]

The flapper air box instructions tell you to lengthen the accel pump rod by 5 mm over the stock length. It would be nice to no what the stock length is to establish a baseline.

I gotta tell ya, I'm not sold on the YICS. I removed it to see if possible leaks were contributing to my running woes. The surge, stumbles, and fading idle at lights are present with and without the YICS installed. I don't have access to a dyno to compare peak power, but it doesn't seem to make any difference in driveability.

[Tiger]

I gotta tell ya, I'm not sold on the YICS... but it doesn't seem to make any difference in driveability.

;D :D :D :D :D :D :D :D...welcome to the club, LOL.

            8).......TIGER....... 8)

[johnclemens]

I'm not sold on the YICS either.
I should have stated that better.
If your YICS is still on the bike make sure you have no leaks in the plumbing. If its gone be sure to plug the holes in the heads.
I do not have it on my racer. I remember on my street bike if those hoses had cracks then it ran poorly and off idle was not smooth.
As soon as I replaced those hoses it would run better. I never took off the system on my street bike.

Who cares where the stock setting should be on the pump rod. Take a measurement of the threads showing. Then go for a ride. Be very sure your all the way up to normal temp. Then adjust the rod half of turn or so. ride awhile and see if it changes. Stop and adjust another half of turn. I would continue in the same direction till it either runs better or you get to the end of the rod. If it still isn't right adjust it back to the measurement you took and then start the process in the other direction. I would ride 5 miles or so at least between adjustments.
Remember this is with CLEAN carbs. If all the passageways in your carbs aren't clean your wasting your effort.

[Night Vision]

I would agree with Rick. You can mess around all you want with jets and not solve the stumble.

the thread topic was drivablity

I'm was not suggesting jetting to cure "plant yo face on the tank / clear n syc yur carb"' stumbles.. more of a tweaking your mixture to rid of surging... maybe hestitation would have been a better verb 

[dpequip]

I'll add my 2 cents worth.  I worked at a Yamaha dealer in the mid 80's when we sold 82 Visions brand new in 84' & 85'  I was the Vision setup guy because no one else there could get them right.  I have some notes from the Yamaha Tech rep back then that I will try to scan and post. We always replaced the following parts when we took new bikes out of the crate:

Fuel Tank if any rust was present
Install the Vacuum Flapper kit
Clean Carbs

Then I would set them up with the following specs.

Once warmed up at idle (1300 RPM) CO (Carbon Monoxide) was set to 2% using the idle air screws and an exhaust gas analyzer.  This was critical to get rid of the stumble.  Unfortunately most of us don't have an EGA in our garage which makes this impossible to set.  If it is ever set correctly at 2% don't ever touch the idle air screws again because if the mixture is off at idle something else is wrong.  This setting is a big deal in getting rid of the stumbles.  Yamaha stated this at the time.

Verify the accelerator pump nozzle is spraying BETWEEN the throttle plate and the bore wall.  If it is not, carefully bend the nozzle and recheck until it sprays correctly.   If fuel spray hits the plate or wall stumbles will result and all the other adjustments are a waste of time.  Every new bike I saw this was never right from the factory.  I adjusted everyone.

Set the Accelerator pump adjustment rod length to a minimum of 50MM (Range 50-60MM recommended)  Measure the distance from the centerline of bend in the rod to the adjuster on the opposite end of the accel pump rod.  This adjustment can loosen over time so use blue loctite or clear nail polish to hold the adjuster in place.  My bike got stumbly a few years ago I found the adjustment had changed to 45MM.  Resetting this to 50MM made the problem go away.  I tried to always set this to the 50MM setting as other settings either cause stumbles or will reduce fuel mileage. 

Synch Carbs after the above adjustments this is important.

Verify 18-20 CM of mercury vacuum are present.  18-20CM of mercury are required for the vacuum operated airbox flapper to work properly.  If everything above is correct this vacuum setting should be correct.  The other cause of low vacuum could be low compression but we were dealing with new bikes so this was not an issue.

Verify there are no leaks in the YICS box.

Verify the Emulsion tubes are spotless clean

All other Jets were stock as we were selling new bikes that had to confirm to emissions.  Stock jets with the stock air box and exhaust system will WORK CORRECTLY if all the setup is right. 

I've owned my Vision since 1984 and it is as right today as it was in 1984. Premium gas is good idea.

[Re-Vision]

dpequip,Do I understand that the Vision stumble can be eliminated (assuming everything is clean and functioning properly) by adjusting the accelerator pump adjustment rod length until the stumble goes away? Will the carbs need re-synching after each accelerator pump adjustment?    BDC

[QBS]

dpequip, your posting is a welcome piece of information, especially for low mileage bikes that haven't had their fuel systems ravaged by the hand of man and miles of road.  It needs to locked on the board as a must read. Thank you for following this thread and making this contribution.

Can you make a case for jetting V carbs richer or leaner in some way to enhance drivability?