High Idle Problem again....

I have a bit of a puzzling issue here. Whenever I open up my bike to 45mph or higher for a long period of time, the idle seems to get stuck around 3k RPMs, so when I pull up to a stop sign, they won't drop down.

I have checked the screws for the butterflies and 1 and 2 seem to be almost exact but 4 seems to be closed more, but only by 3/4 to 7/8s of a turn. Could that butterfly be causing my issue, or could it be something else. I don't have a problem riding my bike around town at all....

 

update...

I just reset my butterflies to 2 1/2 turns out and it appears that carbs 1 and 4 are about sync'd as well as 2 and 3 being close. Am I missing something here? Is this some indication of a vacuum problem somewhere else in the bike?

 

I had to go to a bicycle shop and get some cable spray...... most likely a carb issue, but process of elimination

 

I have been through the carbs a couple of times though...

 

I've been through my carbs about 6 or 7 times now and I'm still finding interesting issues cropping up now and then. That varnish that builds up from old gas has a nice habit of popping loose well after you've thought it was cleaned out and clogging stuff up!

 

I keep finding the same thing. I am beginning to think the varnish has soaked into the float bowl gaskets and it gets reconstitued just enough to gum up the works again after I have reassembled the carbs. I may have to replace the gaskets to make sure, as I keep having idling problems. I think it is caused by the varnish re-depositing into the jets. I wish someone made rubber gaskets instead of the cardboard type ones.

 

Mine does it too. Very irritating. Especially after being into the carbs several times. AND battling a lean popping at highway cruise...

 

Intermittant Airl leaks .. unlikley it's reconstituted 'varnish'
Rebuild OR replace your Vacuum Fuel tap monstrosity and Check for cracked Intake boots (Although I've not personally seen such) Check butterfly shaft seals for airtight ness.

 

Butterflies are not set by "turns out". I believe you are referring to the mixture screws. There are 3 screws to adjust synchronization of the butterflies and they are located between the carburetors on the butterfly shaft. The mixture screws are on the top front of each carburetor next to the enrichment plunger.

My guess is you are quite lean and have compensated by having the throttle stop screw too far in. When the bike gets good and hot a lean mixture burns better and your rpms go up. It's also possible your carburetors are out of sync.

You need to perform the following steps:

1) Make sure the carburetors are squeaky clean, especially the idle circuits, and that the air jets are installed in the proper locations.

2) Check your valve clearances. You cannot successfully set up your carburetors if the valve lash is out of whack.

3) Synchronize the carburetors.

4) Set the mixtures so that the bike idles on the idle circuit rather than the mid range circuit. After doing this you may have to readjust the synchronization.

 

You can't eyeball the Sync Screws, or turn them so-'n-so turns in or out.
The Sync Screws are used to Synchronize the opening and closing of the Butterflys all together.

You adjust those screws to sync the Carbs.
You adjust them on the bench to Bench Sync the Carbs ... and, ...
on the Bike, hooked-up to a Vacuum Gauges for syncing to vacuum.

Other than that, adjusting those screws amounts to "De-tuning" the Bike.

You should do an accurate Sync.
Your problems are all related to Sync and Idle Mixtures I would hazard a guess.

 

After I sync'd carbs 1 and 2, I then counted the number turns until the screw bottoms out to get an idea of where the butterflies where sitting and they were about 2 1/4 turns out when sync'd. I then checked carb 4 and that was 2 3/4 turns, meaning that butterfly was closed slightly more than the others. I thought on this is that I have a low vacuum pressure on #4 because I am having a hell of time trying to get the pressure up on that cylinder.

But my other thought is that #4 was keeping 1 and 2 open which was causing my RPMs to rise...

Edit... I don't think I am running two lean as I am about 3 1/4 turns out on the mixture screws and I have good stable idle.

 

I think my problem is with my #4 cylinder having low pressure..

 

Unless you have both gauges calibrated your syncs not gonna be right.

So what are the compression readings on all cylinders ?

Where are you located in MI anyway ?

 

I have 3 of the carbs sync'd just can't be #4 to sync up. I haven't done the compression check yet.

Saginaw...

 

Try syncing 4 to 3 and then 1 to 2

 

I will try that this weekend....

 

Maybe the Sync Screw is stripped.
That happens a lot.
You try and make an adjustment and the Screw won't take the tweak because the threads are shot.

Maybe you should try changine the Sync Screws around.
Swap 1 & 4
See if having some different threads in the linkage helps.