More carb stuff: Idle mixture adjustment not effective.

[pinholenz]

A number of forum members have mentioned that adjusting their idle circuit screws has made no difference to their revs. Today the same has happened to me. What is this a symptom of?

My newly stripped and cleaned carbs are giving me easy starting (enrichening only) and a steady idle. Today I dropped the idle revs down to about 900 revs. Stayed steady. I then adjusted the idle circuit screws.  (Bottom screws at the base of the carb) Screwed them both fully in. No change. Screwed them out to about 5 turns, no change. Left them at 2.5 and 3.5 turns respectively. Roro and a couple of others have reported the same symptoms in the past.  What does it mean?

Thanks

[Rick G]

 More than likely something is still plugged up in the carbs  Or there is a small air leak . I would vote for the plugged up problem.

[Rikugun]

I experienced the same problem you're having. I find that even well sealed and clean Vision carbs do not respond like other carbs to mixture adjustments. My thirty year old 3.5HP Briggs powered push mower is more responsive to pilot screw adjustments than my Vision!  :P  If turning them to fully seated has no effect then the engine is not running solely on the fuel provided by that screw.

There could be several reasons for this. If it's not idling slow enough, it will be pulling fuel from the transition holes as well. Adjust the mixtures at the slowest speed the engine will tolerate without triggering the low oil light.

Another reason may be a vacuum leak. This will cause the idle to increase and it will find the additional fuel it needs again from the transition holes. Even if the pilot screw outlet is plugged or the screw is closed the engine will find fuel from somewhere and my guess is the transition holes. The pilot jet feeds both the transition holes and the mixture screw outlet. Closing the screw completely does not block fuel from the transition holes.

Test for vacuum leaks with the engine and carbs at running temperaature. Don't just warm up the engine a bit. Take it on the highway for 6 miles or so. Remove the YICS and plug the engine ports to eliminate it as a possibility. Idle the engine and spray carb cleaner where the throttle shafts exit the carb body on both sides of the carb for both carbs. Note any RPM changes.  Hold the RPMs @ 3K and do the test again. Do the same tests and aim the carb cleaner all around the rubber manifolds and where they meet the head surface. What happens?

[Jimustanguitar]

I found a flaw with the carb body itself. http://ridersofvision.net/rovforum/index.php?topic=14448.0 will get you more details. In short, my bike was flooding the rear cylinder with gas and after testing the usuals, I found that my rear carb was slowly dripping gas out of the transition holes (the little tiny ones below the butterfly). The concensus seems to be that one of the brass tubes pressed into the casting has corroded and has a pinhole leak. I bought some POR-15 tank sealer to put a drop or two on the oxidized tube and hopefully plug the hole without plugging the tube, but I haven't done it yet to know if it will work or not.

I also learned that it's pretty important to sync your carbs before and after tuning everything else. After you get one thing dialed in, doublecheck the others. Go through the whole process over and over until you make it through the whole procedure without having to change anything.

[Rikugun]

Jim I'm curious to learn how your proposed repair works so let us know. Any pics would be cool if possible.  :)

Good tip regarding carb syncing. Always do it after a valve adjustment too. I usually do the sync and mixture adjustments together and leave the sync tool plugged in the whole time. You usually need to go back and forth between mixture and balance anyway. Each cycle gets closer and closer until it's either perfect or close enough to where you're satisfied.  :P

[pinholenz]

Many thanks gents. This will give me start to get back into it. Its rideable and pretty enjoyable at that. But I'd like to improve it some more so it accelerates without the stutter.

Jim that link to your discussion last year was helpful and I even got a wee glimpse of what might be happening in the Vision carb from that very clear CV description. The stainless grub screws to replace the cross head screws on the carb look great BTW

In summary.  a. cap the YICs ports at the manifold. b. sync/adjust/sync/ adjust again. c. adjust should be at the lowest possible idle. d. carb clean spray  at low idle (especially butterfly shaft ends) AND at 3k RPM to check for leaks.  e. take a good swig of patience. f. start again if not improved.

[VisionMeister]

Check your enricher plungers sealing face with a magnifier. Look for any nicks that could be letting small amounts of fuel to be sucked through when closed. Make sure they are fully seating when reassembled.
My eye sight was not good enough to see this when I was pulling my hair out chasing carb demons.

[Rikugun]

Another good tip, nice!  :D Even a maladjusted cable (too tight) could be mucking up the program while trying to get the mixtures adjusted.  :(

[fret not]

For those of us who are experiencing diminishing acuity of eyesight here is a clever trick, use a digital camera to take a pic of what you need to see, like the numbers on a jet, wear patterns on a part,  or anything very small.  This is especially helpful with jet sizes.  With the digital camera you can zoom a bit and clearly see those smell things that otherwise would be elusive.  I learned this at the Bonneville salt flats.

[Rick G]

I use a jewelers loop that i bought at Harbor Freight , 10 years ago, its great for reading jets or ring sizes.

[The Prophet of Doom]

you can zoom a bit and clearly see those smell things that otherwise would be elusive.

A good tip for those elusive smells

[fret not]

Yeah, Roro, good catch on the typo.  I just noticed it myself. ;)

[pinholenz]

This time I had a go at synching the carbs with the YICS ports capped. (Rebuilt YICS is still leak free) Surprised to see the idle RPM drop as a result. The more I thought about this the logic of carb synch and idle mix being related dawned on me. (My hard-drive is nearing capacity and the brain is a bit slow)  - Unless the sync is right, the idle mixture will be skewed and vice versa. - Doh!

Sure enough, as I approached synchronised vacuum, the idle mix adjustment screws started to respond to adjustment. I kept tweaking synch/idle mix/ idle speed for about an hour until the bike was overheating and the fan kept running. I left the YICS ports capped and took it out for 100 km run today. Lovely crisp exhaust note and only a slight hesitation when the throttle gets cracked open hard off idle. Nearly there.

I'll do another round of tweaking the 3 variables before having a go at adjusting the accelerator pump rod again. Then decide if I really want the YICS re-attached.

Apart from being a nice idea and a point of difference, what difference does the YICS actually  make to performance/economy/longevity?

[Tiger]

Apart from being a nice idea and a point of difference, what difference does the YICS actually  make to performance/economy/longevity?

::) Oh bugger...a YIKES question ;D :D :D :D :D :D :D

I removed EVERYONE on my 22 Vision rebuilds, that's how much I rate the YIC's system ;) However, some Vision owners will obviously disagree with me :o ;D :D :D :D :D :D :D Its your call really.......

Whenever I work on rides, I ALWAYS use a large box fan...and with both garage doors open... to allow cool air to circulate the motor. Works for me, no cooked motors!!

                             8) ....... TIGER .......  8)

[Rick G]

Jason Morris , explained it best. The YIKS was designed for the 4 cylinder bikes, and made little difference  on the Vision. . I junked the thing long ago  and never looked back.

[jefferson]

Tmyth79 got good results with his metal replacements. I like the mpg increase he is seeing with his unit. Like to see more results from other people using them. I tend to think a properly funtioning yics is a benefit to the running etc of our bikes. The theory is just like the pressure waves in a 2 stroke expansion chamber. In practice they should have used better quality boxes and non-collapsible hoses. Tmyth79 has the unit with long metal tubes and short hoses. I think that would be the best way to go.

Jeff

[Rikugun]

I've never had a properly working YICS and now run with it off so I can't comment on how effective they may be. Claims of power increases based on "seat of the pants" instrumentation I'm admittedly skeptical of. Results based on measurements (such as mileage gains) on the other hand tend to get my attention.  :) I too would like to see more corroborating evidence.

[Rick G]

My experience with the YIKES box , as to millage , was there was no difference . I got close to 50 mpg with or with out , on the hi way.

[Rikugun]

Rick, that goes hand in hand with a Cycle World article I read long ago where they claimed the YICS was most effective at idle and maybe into slow speed operation. Once engine speeds and subsequent mixture charge speeds reached a certain level, as far as the engine was concerned the YICS was no longer part of the equation. If this is true, one would think mileage would not be greatly affected by removing it unless stop and go traffic were the bulk of operation.