i have an intermittant problem with my 3tj/t/cat hybrid thats spoiling every ride.when its cold the engine idles/revs cleanly but when it gets hot the revs and the idle hang anywhere from 3000-6000 rpm.i thought it must be a vacuum leak with the carb intake rubbers so i changed them for another set,i checked the throttle cable tension and lubed the cable,i also resealed the 3tj/4jh airbox as it had a few gaps in it after a couple of years all to no avail.my last thought makes me think its a sticky or out of adjustment valve allowing fuel air mixture in after the throttles closed.im running a 3tj airbox with a 4jh bottom part where the carb rubbers go plastic welded to the bottom of the 3tj airbox,another thought was a leaking petcock(ooer) as the tap does weep slightly.anybody had any similar problems as this is driving me mad.i love this bike but my patience is starting to wear thin and i cant afford to lose anymore hair!

Have you balanced the carbs? I had a similar problem and did a quick balance of the carbs and now it's lots better.

Here's how I did it (cut a pasted from the PB forum)-

"Well, it's not as exact as using the proper gauges but it works and it gets the carbs in roughly the same postcode if they're miles out (mine were).

I used 0.6mm wire, other wire sizes are available.

Do the left side first (I'm assuming a generic IL4 lump but I suppose it'd work for most carb setups). You need to be able to move the slides with your finger so take any bellmouths off that might be there. You need a couple of lengths of wire long enough to reach under the carb butterflies, with enough left over to put a 90 degree bend in (so it can't drop down through the carb!)- about 150mm should do.

Crack the throttle and slide the wires under the butterflies in the carbs. One wire will be gripped tight and the other will be slightly loose if your carbs are as out as mine were. Adjust the linkage between the two left carbs until both bits of wire are held by the butterflies.

Repeat the step for the right side carbs.

To balance the two pairs of carbs, crack the throttle again and put one piece of wire under the butterflies in carbs 1 and 3. Again, if your carbs are as bad as mine were, there'll be a definite difference in how tightly the wires are gripped by the butterflies. Use the main adjuster to balance the two pairs of carbs to each other.

It works, it's quick and dirty and is better than not doing it"

It only takes half an hour or so, and you can do it with the carbs in-situ- good luck!

I'm sure you've cleaned the carbs but that would be my first thing then balance them.

thanks all,gonna borrow some vacuum guages and give them a balance,thevye not been balanced for over a year-i knew id forgot something

balanced carbs today,and just as bad.i reckon it must be a valve that needs adjusting so the motor from the track hybrid is going in the road one so i can still use it while i do the valve clearances.i was going to swap them anyway as the track hybrid motor has only done a few thousnd miles from new whereas the road motor is just coming up for 24000 and the clearances would need doing anyway.it will also let me change the rads over as the road one got bent when i hit a dog last year and also do a clutch swap too.cue a few late nights in the shed!!

managed to get the motor from thre track hybrid into the road one without too much drama,swapped the rad,carbs,and downpipes too.checked the valve clearances and they were all within tolerance on both motors though a couple were close so im gonna do those while the road motors out and then put it in the track frame.should be finished tommorrow hopefully so i can get some riding in.

got the old girl fired up and running-sounds sweet!just gotta rivett up the chain connect the clutch cable and clean out the sprocket housing of all the gloopy,manky chain lube and maybe give her a road test tomorrow.im too knackered to do any more-in the shed til 1am last night,then couldnt sleep-wont be a problem tonight!

Woo!

Have fun, but be careful

cagiva996 wrote:,another thought was a leaking petcock(ooer) as the tap does weep slightly.anybody had any similar problems......

i had similar problems with my fuel tap, the tj one is plastic and to be honest crap after 20 years, so i took it apart and re-built it with the bit's from a GS500 slingshot (you know the learner bikes )
threads here
viewtopic.php?f=37&t=22957

out of interest
if the carbi balancing made no difference, do you think it was just the valve clearances or have you done something else
my valve clearances weren't that far out, but i needed to change 3 shims then balanced the carb's and it was like i new bike

i checked the valve clearances on both motors and they were all within tolerance(though a couple were close) and its still hanging the revs up even with the low mileage motor in,its not as bad but still bloody annoying,im going to balance the carbs from the track bike to elim inate all possibilities.the track t/cat motor ive put in has only done a few thousand miles and sounds so sweet.thanks for all your help and advice guys top draw as always! ill keep you all posted.