After the bike has warmed up the idle will occasionally surge up to 3000 RPMs again and then come back down after a second or two.
I took a video to see if anyone has encountered this before and can help me identify the problem.
Please comment if you have any suggestions.
Note: I did not touch the throttle in this video.
I know you have been through all this, but that surging idle screams air-leak. Does that bike have a vacuum operated petcock? Just trying to think of weird air sources.
ReplyDeleteWhere is the airbox/filter on that bike? Maybe some weather stripping to seal it up would help.
Another possibilty, though remote, is that the throttle cable is snagging on something. You didn't touch the throttle or turn the bars though, so probably not.
Where does the choke lever/knob sit on the bike? Maybe something it triggering the choke to cause it to surge.
Is compression even across the cylinders?
Compression is good. No leaks at the air box.
ReplyDeleteI have since found and solved 2 air leaks. But every time I find one, a new one pops up and symptoms return, just exhibited slightly differently.
Now I'm trying to determine if the #3 carb has an air leak at the manifold boot or the throttle plate dowel.
There is a valve on the top of the 'Air Box' (plenum) they call the 'air cutoff valve', it's the same thing the automobile makers used to call a 'deceleration delay valve' - anyway, it's mounted just below the breather and to the front, and has a vacuum hose going to the #1 carb. You might try disconnecting the hose and plug it and see what happens- also apply vaccum from another source if you have a 'Mighty-Vac' or something.
ReplyDeleteThis valve also must be removed to R&R the carb set and the o-rings there might have been left out on re-assembly.
I have run into this and all manner of other uneven idle conditions on these- just do your self a favor and get hold of the vacuum guage setup for synchronizing your carbs before you go much further with anything- it's incredibly crucial and you'll be glad you did!
I've confirmed that the problem is not the air cut off valve several times, and the o-rings are in place.
ReplyDeleteI've got a set of vacuum gauges that you can see here:
http://gnarlywrench.blogspot.com/2011/10/two-steps-forward-two-steps-back.html
I've also got a mercury manometer that is not pictured.
Thanks for your comment!