Strange Idle problem

Hey everybody! Glad to be now a member of these forums! I am now a proud owner of a XJ 650 1983. Great bike.

Now, on to this mysterious problem.

The bike warms up and idles perfectly. The throttle cable and enriching circuit cable are fine and dont stick at all neither cold or warm. I sprayed all around the boots and pretty much everywhere around the carbs with WD-40 to check for vacuum leaks to no avail.

The Bike idles perfectly at around 1100-1200 RPM. Only when I open throttle a bit more the RPM gets stuck at 3-4k. While this was happening I again checked for vacuum leaks and the cables. Everything was fine.

Even while it is doing this, I can just shut the engine off and switch it right back on and it will idle fine at 1100-1200 RPM again.

Any help would be GREATLY appreciated! I really dont feel like bringing the bike to a shop!

thanks ALOT in advance!

If anyone wants some pics or anything go ahead and ask

 

When it goes to 3-4K, have you tried pushing the throttle shaft closed with your finger between carb 1 & 2?

I would try that first. The next thing I would try is to back off your idle adjustment to see if that does anything. If mine is too high, it will hang coming off of high revs. When you checked for air leaks, did you do the throttle shafts? Make sure you check those for leaks too. I listed these things first since they can be done with the carbs on the bike.

If none of those things help, The next thing I would check is to see if the pistons in each of the carbs have a good clunk. Search for 'clunk test'.

Just some initial thoughts...

 

do a search for "clunk test" then thank Mr Rick-o-matic

 

could be running lean, carbs been stripped/tinkered with before you bought it? could be the pilot screws needing adjusting..

warm the bike up, turn the idle down to about 1k and adjust each carbs pilot screw one at a time. Need to turn it out until you hear the revs peak, then turn it back an 1/8th - 1/4.. rest the idle back to 1k then do the rest of the carbs.

Then again, it could be something else.

 

ok so im going to do all those things and report back to say if anything worked except for the clunk test. This may sound silly but I cant find it anywhere.. If there is a precise link detailing what the clunk test is it would be very helpful. But yes the carbs were stripped and somewhat tinkered with before I bought it. Ill try to post up a pic of them later. Honestly Im not even sure if its the stock carbs. I have the yamaha repair manual but i cant tell because the pictures are very old

 

Here's a few pics of my UK 1982 XJ650 if that's any help.

http://img.photobucket.com/albums/v407/ ... ace_25.jpg

http://img.photobucket.com/albums/v407/ ... ace_26.jpg

http://img.photobucket.com/albums/v407/ ... ace_27.jpg

 

Well, just by looking at your carbs in the pictures I can tell that you should swap carb float bowls 1 and 3 - the drain plug are in the wrong direction otherwise.

Anyway, I had a very similar problem with my bike which seemingly got solved by simply rechecking the fuel line coming from the gas tank to the carbs. Just something to look at...

 

Weiss,

Are you going to pull the carbs?? If you do check the throttle shafts for binding. Open the carbs slowly and close slowly and look at the butterflies and see if you can see any binding. We had that happen to two sets of carbs we were working on. We changed throttle shaft seals and had a slight bind on one carb. That was enough to hang the idle up there like you are saying. Just my thoughts. Hope this helps.

MN

 

I am going 2 tell you how to fix this problem. Loosen your throttle cable a little at the throttle.

 

i have an 82 maxim and my bike was doing the same thing. Enstead of doing all that unneccessary work just loosen your throttle cable a little at a time until it stops. But dont do it at the carbs do it at the throttle itself.

 

Just to say those arent my carbs lithdoc haha those are another user's carbs. Well, I checked everything and everything is fine. I just remembered that the last owner told me something about "reving it up when it idles high to even pressure in the carbs". Tried it out, just give the gas a quick jerk and release just enough to raise the rpm and it comes back to normal. So I now can officialy live with it without geting stares at a stop. But what could be causing this? Some gunky valves or I donno what? Maybe this has something to do with the modifications he brought to the carbs? Anyway in this link are some pics of the carbs (still on the bike) and the bike

http://s655.photobucket.com/albums/uu273/weissmikael/

 

If you are going to be reving it up like that you can say goodbye to your crankshaft bearings soon.

 

I'm betting on a throttle shaft bind myself. Pods make it so EZ to pull those carbs and check it out.

 

I don't need to rev it up much, doesnt go higher than 5.5k rpm for sure. Just has to be jerked real fast and let go as fast and it does the trick.. is that still bad?

 

I dont think revving quickly and letting go will be to much of an issue, but it would be better to just get it right and then you will not have to do that. Just out of curiosity lossen the throttle cable like I was saying earlier and let us know what happens.

 

Alright, its dark out right now so I cant do much, but tomorrow Ill go and loosen the throttle cable and check again for a throttle shaft bind. Thanks for all the help and suggestions till now guys, Ill keep you up to date

 

OK well I just lubed the throttle shaft real good and it works fine now! Thanks for your help people

 

i've been having the same problem with my bike. i was test riding to check out my brake job (to see if the discs warm up or not) and noticed that it would idle fine. i could give some throttle and sometimes it would drop back down to idle revs and other times it would hang at around 3000. i could get the revs to decrease if i left the clutch lever all the way out and hit the brakes a little bit. once the drag brought the revs down they would stay down.

the throttle doesn't seem to be sticking.

after obsessing about it all day at work yesterday (i.e. scouring this forum) i believe my bike will fail the clunk test. at first, i was thinking an air leak might be the culprit. but after thinking about how the propane vacuum test works - i shouldn't see these symptoms unless i was riding through some propane.

however, it makes sense to me that one or more sticking diaphragms would basically simulate (from the perspective of the cylinder) the exact same test.

this also seems to jive with plugs 3 and 4 being fouled this spring while 1 and 2 looked very good.

hope i'm right. will report back with results.

 

took carbs off and cleaned them. found one potential clunk test faIl. found a clogged pilot air jet. two of the floats were very dirty - took some doing to get the pins out.

put 'em back on and its worse - climbs up to 5k without touching the throttle.

must say i'm at a bit of a loss.

UPDATE: SOLVED! when i reinstalled the tank after the brake job - i had mis-routed the throttle cable. it put just enough pressure to have the throttle open slightly. re-routed the cable and problem solved.

at least i got my carbs cleaned.