Xj650 HIGH IDLE, puts itself to full throttle

Okay, been a couple months since I've posted, I left the bike alone for a while. It was doing great until I changed the air filter ages ago, that caused me to notice an air leak. I replaced the throttle shaft seals to fix the leak (i used to starter fluid to figure out thats where it was) and now the bike thinks it needs to go full speed all the time. When you turn it on it runs 5k rpm. The idle speed screw (the one in the center of the carb rack) even all the way out (shouldnt idle at all, it should die) still starts it at what appears full throttle.

What its not:
Its not the accelerator getting stuck or any of the butterfly valve getting stuck. They work fine, have checked them multiple times. They are all at the exact same level using the index cards as suggested and open and close just fine.

Any suggestions? I've had it apart 50 times trying to figure it out, Seems WAY too problematic to be a sync issue or anything. I mean, if it was out of sync it might idle a little high or die right? not run at 5k rpm ALL THE TIME. Does this seam like a symptom of too much air or too much gas? From what I read air leaks (lean mixtures) cause higher running speeds, therefore maybe I have a leak. But wouldnt it have to be massive to cause this? all of the carb-head boots look great, they all look brand new, not a nick in them. If a float gets stuck and leaks gas into the block, wouldnt it not start? Im making sure thats not my problem. It doesnt appear to be, I dont see excess gas anywhere, but I was wondering what I would see if that happened.

Thank you for any help.

 

Be sure that you've re-tightened the throttle cable nut at the handle. I forgot to tighten this puppy up after installing the carbs and she revved to the sky.

I know you said it's not getting stuck, but this is slightly different.

 

do you mean the nut on the actual cable up by the grip? That was not touched. Only been playing with the carbs. And the actual throttle pulley on the carbs is going all the way back down and the valves are closing is what I was trying to convey. Sorry for the confusion.

 

That's ok, just a thought. That is the nut I'm talking about, I loosened it to give some slack while I removed the throttle cable from the carbs.

 

I wanna say air leak too, but from the sounds of it, you've kicked that dead horse around for a while now. But have you tried the propane air leak check? I had an air leak I couldn't find for the life of me, but was able to find it with a small propane torch. My leak was small, and mine was still jacking up to 5k or more. Especially when the bike was running causing vibration and it would be at like 4k or so then I would rev the bike trying to get it to drop down, and it would hop up to 5k or more due the vibration causing the small air leak to flutter and get bigger I presume.

I assume you've checked the jets, and the floats not sticking, cause yes a stuck float, should flood out, but a misaligned one may be closing too late thus causing the bowl to fill up too far but not overflow. Try the clear tube method to check how far your bowls are filling up.

On a side note. This is the method I use to bench sync. However, I found paper clips a tad too fat, so I used the "B" string off my guitar.

http://xj650.blogspot.com/2009/04/how-t ... carbs.html

 

Im interested in this propane test as an air leak is still the best suspect. How does it work. doing a search I see many people saying to try it, or saying they have tried it, but no real tutorial on what I am to do.

Thank you!

 

It's easy. Just don't light the torch! haha

I used one of those little hand held ones and turn it on just a little, and then fire up the bike. Then slowly put the tip of the torch in and around the carbs & boots. The idle will pick up if it sucks in some propane. I ended up finding the general area of the leak, and the boot in suspect. I then taped a straw around the tip of the torch to narrow the propane stream, and get in the tighter spots (with the bendy part of the straw at the end so I could bend it in a bit to check the harder to reach spots)

*EDIT* On a side note, since your bike is idling so high, I would highly recommend you put a box fan on high right blowing on the front of the motor. Bad enough you've got an idle issue, no need to burn anything up and compound the issue.

 

Did you ever figure out out? I'm having the same problem with my 81xj650

 

He's long gone!

http://www.xjbikes.com/Forums/viewtopic ... rt=15.html

 

What's been done so far?

-Valves in spec?
-Carbs thoroughly cleaned and serviced, all worn parts and tiny o-rings replaced?
-Float levels accurately and individually wet-set to spec?
-Bench sync?
-Running vacuum sync?

 

whose long gone?

Im not much of a mechanic. I finally gave up and had a shop look at it. They couldnt get it tuned either. it would work for a while and then slowly start to idle high again. Finally bought a another set of carbs and they tuned those just fine. She's still running.

 

whose long gone?

Im not much of a mechanic. I finally gave up and had a shop look at it. They couldnt get it tuned either. it would work for a while and then slowly start to idle high again. Finally bought a another set of carbs and they tuned those just fine. She's still running.

 

Throttle shaft seal.

Glad to hear you at least circumvented the issue.

 

Hated to do it that way, but I did want it running again. I kept the old ones with intentions of fixing them, but its yet to happen.

 

Good to hear you got it running.

I replaced my throttle shaft seals, float needles and seats, wet set the fuel height to spec, bench synced, valves are within spec, checked all butterfly valves to make sure they seat completely. The idle screw has been adjusted in and out without much difference at all.

I am going to do the running vacuum sync tonight after work. Will it be a problem that it won't idle at the desired rpm for testing without applying the choke?

 

If it will idle on the "choke" then either it's not warmed up enough to sync; or if it still needs "choke" once fully warm (enrichment, there is no true choke) then your pilot circuits are still plugged up.

Did you remove the pilot mixture screws, ensure that their little washers were all there and replace those o-rings?

 

I pulled the pilot mixture screws out and checked to see that the washers and o-rings were still there. I did not replace them because they still looked good, and the o-rings that came in the carb rebuild kit were the wrong size. Put them back in with the o-rings/washers/springs/screws orientation.

For clarification it will only idle on choke even once it has warmed up. I will have to look into cleaning out the pilot circuits again.

It was idling ok before I cleaned out the carbs and put new float needles/seats and gaskets, but would die every time I would stop the bike. Then replaced throttle shaft seals and the high idle started.

 

In order to replace the throttle shaft seals, you had to break the rack. Are you 100% sure the carbs are properly aligned with each other in all directions? Any mis-alignment will cause binding in the "linkage" since it's made up of a section from each carb.

 

Ya, when putting them back together I used a piece off glass to make sure they were lined up. The throttle linkage works smoothly, returns to the closed position immediately every time. Also bench synced and checked and adjusted the butterflies so no light was visible past them when closed.

When I start it up it starts great, but then without me touching the throttle it will rev up above 4000 rpm, and only come down if I apply the choke.

 

Vacuum synced, no change. Removed carbs and cleaned out pilot fuel circuit and it no longer races. Now it doesn't want to start very well when cold.

 

I'm having an nearly identical problem with my 82 XJ750 Maxim.

I broke the rack, replaced all the rubber, gaskets, throttle shaft seals, etc. Made sure all surfaces were cleaned and tiny passages clean.

I bench-synced the carbs, and wet set them within 3mm of the bowls.

Prior to taking them off the bike, I needed near full choke to run. After, the idle screw is entirely backed out and no choke and she starts up and jumps straight to 5K RPMs. Sometimes, it'll chill out at 1.5K rpms, but then if you touch the throttle it'll go up to 5K. If I apply choke (for the sake of testing), it'll die down for a moment and then shoot even higher.

I've been testing for airleaks by spraying down each boot with starter fluid, for lack of propane and propane accessories. I think I have a leaking #3, but it doesn't skyrocket in RPMs, just goes 500-750RPMs higher.

Also, it backfires when shut off periodically now too. I really want to sync the carbs, but until I can get the RPMs down, I fear I'd melt the YICS tool.

 

I ended up shooting carb cleaner through all off the pilot circuit passages. Did it from under the diaphragms and out the mixture screws and pilot jet in the bowls, mixture screws and out, and pilot jet and out. This seemed to clear things up. I had noticed for whatever reason that whenever it was running out of fuel in the bowls(as the gas was disconnected) the engine would race just like you described. This led me to think that when I had the choke opened up it was able to run "normally" because it was getting a proper air gas mixture. Without the choke it wasn't getting the right mixture and simulated not enough gas getting through(racing engine like when gas was running out). Therefore plugged passage unplugged= better running.
On another note, I laterHad a problem with a cylinder not firing, and found a clogged main air jet under the diaphragm in that cylinder.

 

Oh ya, lubed the pilot mixture screw rubber o-rings with lithium grease, and used the same grease to hold the edge of the diaphragms down in their grove when rebuilding.

 

I have the same problem. Bike ran great then one day would not start. Held my hand over two of the air intake parts of the carb and got it to start with full choke then once started it revved up to 5000rpm+ and I had to kill it with switch. Then turned choke off and it started right up but jumped to 5000rpm+ again. I bought a used set of carbs off ebay and installed them and they did the same thing. Please Help!!!!

 

Start a new thread for your bike. Also read In the Church of Clean and The Information Overload Hour. You have a vacuum leak somewhere, and I'm going to assume that you have not checked valve clearances, rebuilt your brake system, or done any of the other things that need to be done to a older motorcycle.

 

I practically rebuilt this bike from the ground up and have dumped close to 3000$ in doing so. This bike ran like a dream for over a year. All of the sudden one day nadda. Thats why I am asking for help. I will check the links you added and thank you. Everything has been gone through on this bike Including brakes.. The only thing I haven't done is rebuild the engine block.

 

Colortuned?

$3000?!
Zoiks!