Uncle

:? Ok so I am working on the '80 XJ650

So far I have adjusted the valves, completely cleaned and rebuilt the carbs including shaft seals and fuel rail orings, painted the carb holders with RTV and rebuilt the starter.

The bike starts like a dream, one pop and she is off running. Starter is as smooth as silk. So what is there to complain about? I'll tell you, after all this the bike will not idle steady. I have tried adjusting the idle screw. It will idle for a while then loses its mind and drops real low to the point of dying. Of course if you give it some throttle it will start the cycle all over again. I benched synched the carbs and the engine sounds pretty smooth and throttles right up. So what can still be wrong? It must be something simple, all the hard stuff is done.

Anyone have any ideas?

 

Sure. You're not quite done is all.

First off: Float levels-- checked "wet" using fuel and clear tubing? If not, that's step one. (Actually, valves are step one but you already did that.)

Now you need to do a running vacuum sync.

 

Fitz

I Forgot to mention that. I did check the floats wet with clear tube when I rebuilt the carbs.

I got a set of vacuum gages so I guess that's next. Doesn't the bike have to idle nice to vacuum synch? Seems like it would be a chicken or the egg contest.
Surely there is a vacuum synch how to here somewhere.


btw... I would not have gotten this far without the guidance from you and the other wizards on this site and for that I thank you all.

Pat

 

Do a TEST with Starting Fluid, Carb Cleaner or Propane Gas, ... Testing the Manifolds, Carb Necks, Boots and Throttle Shaft Seals for an AIR Leak.

Another issue to overcome is this:

When you are CLOSE to being Fine Tuned, ...
Perform ONE adjustment at a time.
You TRACK your progress.
More than ONE adjustment at a time leaves you without knowing which to correct.

Also:

Fine Tuning requires Patience and very, very small movements of the Pilot Mixture Screws.
The Tuning you need to do looks like this.
ONE whole sweep of the Big Hand on a Stopwatch = 60 Seconds.
To make a Final Adjustment of the Pilot Mixture Screw, ... you may ONLY NEED to MOVE the SCREW (In) -or- (Out) the DISTANCE of ==> 3 -or- 4 Seconds.
A "Tweak"
A (My-Nute) amount.

Once you are within the Range of Perfection, ...
>>|||Bad,Fair,Good,Excellent,Good,Fair,Bad|||<<
00000-1----2----3-------4-------5-----6---7-00000 ==> ( :00 -to- :07 Sec.)

 

I had a bad petcock diapram that was giving me a hard time with the idle creeping up (until I rode home @ 4500rpm 35 miles). replaced the diapram and it was corrected. easy fix once I found itl.

 

You're not ready for "fine tuning" yet. You will find a point in your vacuum sync where all of a sudden you hit the "culprit" (in as far as whichever cylinder was running too high/low) and it will smooth WAY out. Then as you proceed, it will get more "solid." It's hard to describe properly; I guess there's a certain amount of Zen involved.

 

I went a hunting on the site and I did not see a write up for non YICS 4 gauge synching procedure. Does anyone know if there is one? I have the 4 gauge blue plate special.

Thanks
Pat

 

skip the YICS tool step and the rest is the same.

 

Same as with YICS except you don't have to block the YICS.

Carb #3 is the "home base" it has no adjustment screw other than the main knob.

#1 is "tied" to #2. SO:

You sync #1 and #2. Then you sync #2 to #3; it will bring #1 along with it. Then you sync #4 to #3. And that's basically it.

Opening a throttle will lower the vacuum signal; closing it will raise the vacuum.

Adjust, blip; adjust, blip. Keep a couple of fans blowing across the motor so it doesn't get too hot.

Once they're all in sync, adjust the idle using the main knob.