Engine wants to race after carb rebuild

I am having problems with my Xj650 RJ 1982. I recently took the carbs apart, cleaned everything, checked jets, et all. reason being that since I have had the bike, there were lots of air leaks, diaphragms were very holy with pin pricks, intake boots not fitting, etc.

With the carbies back together, I did the clunk test, I did the same test with the carbs fully assembled, as the slides came down slowly with a gentle clunk, I bench synched correctly, cleared all the jets, put them back in the correct locations, siliconed up the diaphragms, checked for pinched cables, elevated the carbs to have a straight line, old rubbers and she was sagging a touch. I intend on taking the bike to a mechanic to have the carbs synched, but I am worried that the current problem may have the mechanic say "you have other issues, I cannot synch the carbs" and still charge me for the full time.

The idle jets even have their "O" rings replaced, at 1 and a half turns.
My problem is that I think one cylinder is getting too much petrol, as the bike tends to race up to 4000rpm if the idle screw is adjusted even a little. I might get the bike to idle roughly, but 10 minutes into riding, I pull over because I can hardly change into second gear because it is revving so high! The bike cannot take too much choke either without revving up and down, I find it hard to get it to settle into any idle, high or low.

I thought that getting them synched would fix the problem, but I suspect I have missed something. When riding normally the engine pulls very well, runs much better now! prior to the rebuild the bike idled like a swiss watch, and valves are good too.

Hopefully someone has some experience with this, are the diaphragms too stiff? Is a fuel or air passage blocked? Is this something that just happens when YICS carbs are unbalanced?

help?!

 

Man, if your carbs are getting too much fuel at 1 & 1/2 turns, something could be afoot.
Mine are at 2 & 1/2 turns and still two cylinders are lean.
Have you put RTV where the boots and manifolds overlap the venturis, and checked the boots for cracks?
It may well be an air leak somewhere.
I didn't notice it before I coated the boots with RTV, but after I could see the manifolds pulse in tune with the engine...

 

I saw no mention of float levels being checked using the clear tube method and fuel. Float levels are critical, dry setting is only a starting point.

Depending on what you used to repair the diaphragms, stiffness could be an issue; but I'm more inclined to think you have a float or two that needs attending to.

 

Have you tried to turn the idle screw dow to decrease the idle speed? Check the intake boots for air leaks with a shot of starting fluid? Most likley there is a air leak either from the boots or the rubber plugs for syncing.

 

Did you pinch your throttle cable under your tank. Check that first.

 

It is good to get some feedback for my problem, throttle cable is fine, the idle speed screw is not touching the idle lever at all, and the inlet rubbers are in good condition, already checked for cracks.

I have not checked float levels, as before I dismantled the carbs the bike was idling perfectly, so I am trying to focus only on the bits I touched to trace the problem.

I will try riching up the idle screws to get an even idle, I still do not know why the engine would be racing?

the diaphragms may be stiff, which is why I did the clunk test when the carbs were fully assembled, just to make sure they seated correctly.

cheers

 

sounds like the butterflys are 'catching' not shutting down properly, the fact that the idle screw is not even touching would reinforce this proposition.

 

you already did the hard part, now you want to pay someone to do the easy part ?
the idle rod not touching means that one of the butterflys is completely shut, holding the others open so at idle the best you could get is 3 cylinders. when you give it some gas the closed one starts going and it zooms up
your sync is in the left field warning track, look around on here and make a sync tool of some kind and get the sync in to the short stop
then check the floats then turn the mixture screws out another 2 turns
the idle knob has to control the idle speed
now your getting close

 

Did you break the carb rack apart? You may have got one of the carb conection linkages out of place when they were reassambled. That would keep the idle cam from touching and keep the other three carbs open and your idle speed will be high. Take the carbs back out and check, do a bench sync before reinstalling. Check those float heights.
Try to loosen the throttle cable first, it may be too tight. There should be a little slack in it,

 

mlew, if the rack was wrongly assembled, how would he get anything resembling a bench sync?

 

I did not see that he did a bench sync. Did I miss it? I is possible to get one carb linkage in the wrong place, its one of the mistakes I don't repeat.

 

G'day,

Yeah, I did a bench synch, twice, if it is a fraction of a milimeter out, that may be why I need to get it synched. If one butterfly is catching, or closing fully while the others are open a fraction, then it would mean that my bench synch is not as exact as using vacuum gauges.

I did'nt pull the carbs from the rack, I left them complete. Tonight I will rich up the idle jets one full turn, and gently adjust the butterfly's a fraction at a time.

thanks for the help so far, I hope I get it right.

cheers

 

The bike now idles great!

I riched up the idle jets to 2 turns out, and closed the butterfly screws one full turn each, and hey presto, a nice even idle!

So I imagine, as was suggested, one butterfly was slightly open, and I was perhaps too lean.

now to build my own vacuum gauge!

thanks for the help, and yes I have just printed off Chacal's hint list for carbies for future reference.

cheers