raising idle

[only]

i just cleaned these carbs yesterday and assembled today. the bike runs for the first time!

i could only get one cap off the check the diaphragms, but the one i looked at looked fine, but vinyl-looking??

anyway, carbs were filthy, one main totally blocked, some passages blocked, but all clean now.

did not replace any orings at this time, was just trying to get bike running. did not replace choke or throttle shaft seals.

bike runs, idles, and revs. on its own, the idle will raise up for a minute or two, to maybe 2K, and on its own falls back to idle. if you rev it, it will stay at 2k, and fall back down after a minute or so. i initially thought slides hanging, but the bike will do it on its own.

manifolds are OG and look like shit. but, i do not get the idle to bump spraying with carb cleaner while idling, so id have to say theyre sealing.

removed the caps over the hidden screw up top, backed it out to 3.5 from easily seated. was there another bleed or mixture screw that needed adjusting?

any ideas why the rpm would raise up on its own and then drop? im thinking air from somewhere, and i know i have alot of seals to replace.

 

[HoughMade]

Sounds like a lean condition to me. Since you are 3.5 turns out, sounds like either an air leak, like you said, or the idle air circuit is still a bit dirty. A lean condition can cause the idle to hang high or vary. Besides the idle mixture screws you uncovered and the throttle stop that adjusts idle speed, there are no other adjustments for idle.

 

[only]

Sounds like a lean condition to me. Since you are 3.5 turns out, sounds like either an air leak, like you said, or the idle air circuit is still a bit dirty. A lean condition can cause the idle to hang high or vary. Besides the idle mixture screws you uncovered and the throttle stop that adjusts idle speed, there are no other adjustments for idle.

easy enough. it idles well when its down, but it jumps up on its own, and back down. one thing i did not do when i had the carbs down was set the floats, because i did not know from what to where to set to 26mm. i eyeballed them to be even. where abouts is the idle air circuit? is it one of the smaller jetted holes in the throat of the carb? ive seen a well done drawing here a few times.

the air leak could be from anywhere. guess ill go at it again with the carb cleaner and try to find the air leak that way, all i shot were the manifolds, and to me it was unclear if the idle was bumping or not. ill give it another go.

i cant go beat on it and pull the plugs to read, because i have no front brake caliper, and do not know the condition of the rear drum/shoes. i really need to buy the colortune once and for all, ive put that off for many years. that and a real carbsync.

 

[Jamin Smitchger]

My bike has the same problem, but I am not sure why.

I believe I have the idle screw way too high. The bike will go 20 mph in first gear in idle.

My bike is a definite fixer upper.

 

[Pork Chop]

My idle was all over the shop - replaced the old carb boots and fixed that. Now it is hanging at around 2,000rpm, especially when it has warmed up. I can bring it back down to normal idle by dragging the clutch. I think that mine is caused by being too lean but I am a complete noob to bikes and do more investigation this weekend.

 

[mikeybikey82]

yea you are sucking air, mine was doing the same thing! i "painted" my intake boots with plastidip and made some new gaskets for them, and that fixed my problems.
Mike

 

[vfost]

Ya my bike has the same problem i replaced the carb boots and it seemed to help a little bit but not a lot. Everyone i have talked to seems to think its a vacuum leak. Next step for me i think is replacing the vacum lines from the top of the carb boots to the fuel shutoff.

 

[drewpy]

as said before, these carbs have to be spotless.

I had mine professionally ultrasonically cleaned, best money I spent!

 

[cafedan]

id be careful with that carb cleaner too, that stuff is the devil! unless all rubber parts are removed of course.

 

[xschris]

make sure there are no holes in the diaphragms this will cause the same issue.

 

[monkeyboy]

have any of you guys made sure they are sinked,so they are both closed and they both open at the same time.this is the screw in the middle of the carbs,,if not adjusted one will be cracked open a little while the other is closed,,causing what would sound like a air leak or to lean,,