84 VF750 Idleitis

Hello everyone.
Thanks for all your help getting to this point: The bike is together and getting close.
A recap - the carbs were a basket case and are now mostly sorted out. My main problem was that the jets had been drilled out by a previous person. I am running the jets I had in a set of 83 carbs in the 84 carbs / bike.

Starts easily, I have synced the carbs, didn't mess with the initial idle jet setting of 2 1/2 turns out, except to see if turning them all in a 1/2 turn helped, which it didn't. The problem is that the idle will jump up by about 2000 rpm intermittantly. After a few seconds it will go back down to where it was set. (around 1000-1200rpm) I can't find any vacuum leaks - tried the WD40 trick etc... I may be imagining it, and I didn't time it, but it almost seems to repeat itself on a fairly regular cycle of about every 30 second or so. I am now just wondering if it perhaps that it surges every time the fuel pump cuts in? I can't see why though, because I am sure on the float adjustment and the new needles and seats are good.

I havn't been able to road test yet - I live in a town on the main street so I can't risk taking a crank up the street without getting the bike registered and insured first.

My list of things to recheck includes:
- proper seating of the carb to airbox plate rubbers.
- carb to manifold boots (tightened them all the way down with the engine warm allready)
- WD40 test again
- run with the test tank (no fuel pump)

Any other suggestions would be greatly appreciated.

Thanks
Steve

 

I would check for damaged boots, gen1 was known as the worst model for false idle due to leaks at the boots.

 

Hey Toecutter,
I pulled the carbs.....again, and double checked the boots and they seem OK. I did find the problem with the carbs though: The nylon bushings in the link between the throttles of the front and rear carbs were worn and there was about 1/16" of an inch of play. With very little effort on the rear carb throttle assembly I was able to move it, opening the butterflies on the rear carbs slightly without affecting the front carbs. The spring on the rear carb throttles also seemed a bit weak. I found some new old less worn bushings in my box of spare carbs, and also took another 1/2 turn on the rear carb spring by bending the tang and hooking it on a differant part of the assembly. Put her all back together and now she ildes perfect, even though the carbs are now out of sync. I'm too tired now, hopefully I'll get a chance to sync them tomorrow. I believe what was happening was the rear butterflies were changing position ever so slightly when it was running.
Cheers
Steve