82 Keyster Carb Kit & Accelerator Pump Diaphragm Adjustment

[Cdnlouie]

Ladies & gentlemen,

During my recent carburetor restoration for one of our Canadian Vision buddies I needed to install a new accelerator diaphragm and noticed that the Keyster replacement is 1mm shorter for the actuating pin (in the middle of the diaphragm). I thought that I would make mention of that, to those of you who may use the kits or have someone else put them in. This changes the stroke of the accelerator pump quite significantly unless you do a rod adjustment. (I have not checked the 83 kits for this issue).

I don't think that this presents a problem as long as you compensate for it by lengthening the rod shaft. We have not tested the bike yet with the new setting, but I believe that setting it to engage the actuating pin at the beginning of the accelerator pump stroke (and butterfly throttle plate movement) is probably the best intial setting. You can see the accutuating arm when it contacts the pin head quite easily if you look through the arm slot. A final check to see that the spray clears the throttle plate and the side of the venturi is a good idea.

These diaphragm's are getting old now and the new one can really improve throttle response.

Any other experience on this topic feel free to chime in.

Louie

[Lucky]

i've noticed that, and the 1mm difference is probably due to the 20+ year old one being streched...

[Night Vision]

somewhere in the posts are discussions on the accelerator rod length.

it was suggested or there was a service bulletin recommending that the length be increased to 60mm. I checked four carbs and there was only one that was around 55.

I would presume that anything less than 60mm is therefore stock.
the extra 4 or 5 mm should take care of that 1mm.

I also believe the 60mm length is about the max that it can be lengthened.

[Lucky]

The TSB says no more than 60 mm length on the rod, and the TSB was only for early 82 carbs. there are no published specs on what the adjustment should be.
the TSB is on the CD  :D
--Lucky

[Brian Moffet]

Since I'll be ripping into my carbs soon, I'll try and remember to look at this.

Brian

[Night Vision]

:( I've got to remember that there are those few 83's out there and not all 82's have their carbs "updated" (not that that's not a bad thing)

the 55mm rod length I measured is on an unmolested, non-vac'd 82 carb....
two of the 60mm rods were on vac modified carbs.. one 60mm was on a very molested 82 non-vac carb (DeckBike)

when yamaha came out with the vacuum flapper, the tech bulletin said to lengthen the rod by 5mm (ten turns)

http://www.ridersofvision.net/Technical/Airbox/VisionP4.jpg

you could always measure the squirt.... too much hassle for me  :o

[motoracer8]

I wrote a peice awhile back on the accelerator pump adjustment. You measure the volume of the pump shot, .25cc that is 1/4cc, Measure the quanity at both nozzles, as the little check ball can stick, or one of the nozzles can be plugged, this will make them stumble of idle, as will too much fuel, that is why fuel quanty was reduced on the modified 82's and 83's.

  Ken G.

[Cdnlouie]

Motor-racer said: "...that is why fuel quantity was reduced on the modified 82's and 83's."

If you are referring to an adjustment of the pump rod to increase or decrease fuel quantity (at least within the 55-60mm range) I would have to disagree (at least for the 82's and I am not familiar with the 83's).  I am open to be corrected on this one, but it is my understanding that you cannot change the capacity of the diaphragm, unless you shorten the rod to depress the diaphragm thereby preventing it to fill to full capacity.  I think that Yamaha was trying to adjust the timing at which the pump injects the fuel (when lengthening the rod from the 55mm point).  In normal operation the diaphragm will completely empty on a full throttle opening (depositing its full capacity in the carburetor throat) and that is why the spring at the end of the pump rod is there to allow the diaphragm to finish its stroke and the throttle plate to continue opening to full throttle.

I would suggest that the increase in the rod adjustment was primarily to alter the timing of the fuel entering the venturi. An increase in the rod length would retard the injection sequence. You have to be careful not to advance the injection before the throttle plate opens and 55-60mm gives you some room to do that.  I also think that 55mm is most likely the beginning of diaphragm action and if you did go less than that (55mm) you could actually decrease the amount of fuel as the diaphragm is not allowed to fill (with fuel) to its full normal capacity. I don't see how Yamaha could have decreased the fuel amount by staying within the 55-60mm stroke at least on the carbs I have seen.

In relation to the Keyster kits I am concerned that the 1mm shorter actuating pin on the diaphragm causes a greater retarding of the fuel injection sequence especially if you are already at the 60mm length. I need to actually test this out with a set of carbs using the new diaphragm before I can comment on what might be the best setting.

P.S. Tiger is testing a recent carb set that has the new diaphragm so maybe we could ask him to measure his rod and then when he gets it on the road see how things work out (at the time of his rebuild, I did not think to measure the rod  :().

These carbs are a fascinating piece of work, a true work of art.

Louie  ;)

Ken, I would be interested in the link to your full article so I can better understand where you are coming from?


P.S. I revised this post a few hours later with a bit clearer explanation of what the lengthening and shortening of the rod actually does to fuel injection timing.

[Tiger]

so maybe we could ask him to measure his rod

:o :o :o :o...Oh, I see wot yer mean... ;D ;D ;D ;D ;D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D... ;)

:) I need to fit the exhaust and see how she performes first, but I will certainly let you all know... 8)

[motoracer8]

Louie, Adjusting the rod Does not alter the timing, just the quanity of the fuel. You are quite correct that by altering the rod lengh you limit the amount of fuel the pump takes in. I have not seen one of the after market diaphrams so I can't comment on them. I have been able to come up with oe Yamaha parts, so thats what I use. To set the pump, You must have the float level correct and the carbs full of fuel, Rotate the throttle one of two times to make shure the pumps are working and full of fuel. One complete opening of the throttle is what you measure. The 82's were set at 1/2cc per Yamaha service bulliton, The modified 82's and 83's were set at .25, or 1/4 cc per bulliton 1/28/83 sb m83-003. I have never used rod length measurement, I have always used injection quanity. I have used this methed on several Yamaha carbs, And more than I can count automotive carbs. I use an automotive exhaust gas analizer and set the idle CO to about 3%.
   Ken G.

[Cdnlouie]

Does anyone have a copy of those bulletins?  I would like to figure out what they were trying to do before commenting further?  If you could email them to me or point me in the right direction that would be great.

There are definitely timing issues and fuel delivery issues involved here. If you add length to the rod after the diaphragm has filled to capacity (from the spring load inside & throttle closed), you add space (and time) to close that space between the actuating rod and the beginning of the fuel delivery stroke.  In this scenario the throttle plate moves several degrees before the fuel delivery stroke begins and you can adjust this timing event by lengthening or shortening the rod (that is what I mean when I am talking about timing).  This is true from when the actuating rod is no longer in direct contract with the diaphragm pin.

Now for the confusing part, It is not true when the the actuating rod is in contact with the pin or has the pin depressed, limiting the amount of fuel beling delivered (this is hard to explain and even harder to understand without looking at the pump).

I am interested in the comment made about a bulletin saying the rod was lengthened to 60mm at some point in the Yamaha revisions which can only increase fuel delivery not decrease it as you say was the case in your post Ken. I need to understand a bit more clearly what Yamaha actually did before I can make more sense out of it.

Thanks for your profitable comment,

Louie

[motoracer8]

Louie, I copied the service bullitons from a Yamana dealer's service notes 20 years ago, and the information was along with the modification kits for the 82 carbs. You have got forget about the length of the rod, because rod length will not always give you what you want, that is the quanity of fuel. If you have replaced the pump diaphram with one with a shorter button and not adjusted the rod length to compansate,it will have delayed pump action. You have to start with the pump operating cam right aginist the diaphram button 0 clearence, but not yet compressing the diaphram, that is where you start. At this point a full stroke, or to wide open throttle will give you too much fuel, more like 1cc or more,too much. If you are not measuring the fuel quanity you are shooting in the dark, there is no accurate way of saying this rod length will give you this much fuel. You will find set correctly pump stroke is quite short. The little spring on the rod, beteen the pump cam, and the end of the rod is so the diaphram can bottom and throttle rotation can continue without damage. Early Yamaha Ventures had some of the same issues as the Visions. I used to rebuild carbs for a living mostly automotive, but they all work pretty much the same. Small Webbers and Solex carburettors have the same type of accelerator pump, and they are set excatly as I have described to you, fuel quanity, not rod length. I can only assume Yamaha felt rod length was close enough, and quanity measurement was not nessary.


  Ken G.

[h2olawyer]

FYI:

The TSBs are contained within the parts list on the Yamaha Parts site.

H₂O

[Cdnlouie]

Hi Ken,

I am glad to see that we agree on the delayed pump action point which is what I was referring to as the timing issue. I also agree with you completely about the fuel quanity which can be adjusted by shortening the rod.

Nevertheless, my puzzlement is in relation to what Yamaha was doing with increasing the rod length by 5mm in the early April 82 TSB. It would appear that this was an early attempt to increase fuel delivery (as lengthening the rod must do) or delay the fuel injection process once the maximum pump stroke is exceeded. This adjustment appears to provide maximum fuel delivery available from the diaphragm.

Now, the later airbox and carb modification solved the idle and mid-range issues but it seems that they kept the accelerator rod adjustment of about 60mm as most of the carbs I have seen are adjusted to that range (for better or worse).

Your idea of decreasing the rod length to decrease the fuel quantity is certainly a valid one and as I have the opportunity will do some experimentation with the values you recommend to see how things work out.  When it is all said and done perhaps we will be able to provide an acceptable rod length that is easier for most guys to set up and that coincides with either an original pump diaphragm or the Keyster diaphragm which are going to require different settings.

Thanks for your input on this topic, it helps to develop a better picture of what is going on.

Louie

[motoracer8]

Louie, I belive Yamaha was trying to increase the duration of the pump shot to cover the lean running issues at low and mid throttle openings. When new these machines had a flat spot just off idle, and would surge at small throttle openings. Before Yamaha made available that silly airbox flapper door thing, [that was no more than an intake restriction]  I reduced the size of the air correction jets, to richen the overall mixture, they are the ones that thread into the top of the carb with the emultion tubes, as Yamaha offered no alternate parts, I Made some from Webber auto carb parts as I used to have alot of that stuff around, I found some #60 pilot pilot jets,And 1.75mm air correction jets, Pilot air was left at 1.30mm. They used two different size main jets, 122.5 & 127.5 front & rear, I used 127.5 front and rear, Make shure the float level is about 36mm, Set your idle CO at about 3%. I have an 83 and the carb is alittle different. I use 130 main jets ft & R #50 pilots, 132.5 pilot air, and 1.75 air correction, and I removed the flapper door. I have ridden this machine for more than 20 years, and 40,000 miles, And it's milage is in the high 40's and low 50's if not ridden too hard. The early 80's was the start of the lean running issues for all motorcycles, as they were dealing with emission regs.
Good luck with your carb tuning.

  Ken G.

[supervision]

 Ken, thanks for the information, I'll follow your jetting sugestions, and also the acc. pump delivery amounts  on this set of 83 carbs I'm getting ready for my 82.  I'm hopeing for allitle more power on top from the slight size increase over the 82 carbs.  I can't believe how they made a right turn on the low speed needle adjuster!  One question, do you know if the 83 front pipes are different? I have some if it's a good deal to use them on this conversion. sv                Do you still ride? are you considering comming to Colorado ? 

[Cdnlouie]

Hey there Ken, great research on carburetor settings. Your thought on the air correction jet (non-removable brass insert on carb top) was a keen approach. It looks like the stock setup is almost 2mm and you brought it down to 1.75mm to richen the emulsion tube mixture. Most of us have also increased the pilot air to 130 or 135 and have experienced good results with that setting. Some have changed the front main jet to larger than 122.5 with some degree of success as well (I have kept the original setting myself).

An interesting Canadian phenomenon was that they ran 120 pilot jets in all the Visions sold here. Maybe trying to compensate for the colder temperatures.

Take care of yourself and keep in touch  :),

Louie

[motoracer8]

Louie, Yes I still ride quite alot, The Vision dose'nt get quite as many miles as it use to, as I belong to a British M/C group, the BMW club, and a Ducati club, plus I ride a BSA in vintage M/X. I live in California so I can ride almost any time. When and where is the Colorado event?  I use to go to Steam Boat springs every September for the AHRMA national. I read somewhere, mabe in a road test, that the inner diameter of the head pipes was reduced on the 83's, I don't know this to fact. I found a new exhaust system, with perfect chrome for a 82, so that is what I have on mine. I use the 83 rear head pipe, but the rest is 82. Mabe I'll see you in Colorado.

  Ken G.

[supervision]

 ah so you live in ca. and you ride ahrma. how come you never came to one of our rides, probably too busy. Itoo live in ca. I also like arhma mostly spectating the old bikes, I did ride trials for a couple seasons, I think I went to  cottage springs, sandhil and holister this year just watching and seeing whats happening.  I've been to steambot twice, 94 and 97, camped and had streetbikes along, cb77 and ossa wildfire

[motoracer8]

I've riden AHRMA events almost from the beginning, Back when it was the California vintage racing group. I ride several different bikes, mostly two BSA's a 441 and a 250, sometimes a Honda SL125. I miss Steamboat,the end came in 98, I went for 18 years. My number is 8X, come by and say hello sometime.

  Ken G.