TOPIC:

had that problem on my bike and it was the advancer. Took it off and cleaned it up. Fixed.
Aaron

Just checked the advancer, i think thats what i was looking at, under the round right side cover.
Took the magnet assembly off, and found everything under it looks clean and neat, i gave it a small squirt of lube just in case, but the motion to the right was smooth and snapped right back to place, so think thats ok.

After letting the silicone seal sit over night, and warming the bike up completely it idles at about 1100-1200. Revs up and down fairly smooth, though i think the revs are dropping a bit slowly. It no longer sticks at 4-5k.

Yesterday as i was warming up the bike i decided to check the idle set screw, and found that it was set SUPER high, and once the bike was warmed up i brought it back down to 1100-1200 or so, and thats that. I think the very high idle set screw was causing at least some of the high revs.

On another note - as i was cleaning the carbs i noticed what i believe to be the mixture set screws (i see them on the top of the carb, when looking form above?), a blat head brass screw inside a tight housing. 2 of these screws have their heads stripped (darn). I know these carbs are not synced, and my sync tool is on the way. Is there a way around the air mixture screw when syncing, or does it even have nothing to do with it?

Well, if the silicone got it to stop hanging, sounds like the air leak was definitely the problem. I'm guessing the silicone won't hold too long, but if it does, power to you.

They probably had the idle set high to keep it running with the leak before.

On my carbs (Keihin's), the sync is done by three different screws you can see from the top, but they aren't brass, they just adjust the position of the butterflies in the carbs relative to each-other. And that's what you're adjusting when you sync, basicaly making sure they all open to where they're all creating the same vacuum. I would assume it's similar on other types of carbs, so the mixture screw would be a different thing, but I'm not 100% on this. I'm still learning some about carbs as I go.

Silicone will not hold up to gas for long. I have had good luck with case sealent.

I've just purchased my 82' Z 750 N spectre. i had this happen to me once I'm assuming it's the throttle cable but I haven't had the time to lube it or anything. so I'm hoping that i will have time to asap because in 2 days im taking it for a trip. my first long distance trip on a bike and i barely know her. daring as my venture may seem i have some confidence that she can take the journey, she cold starts like a champ, idle just a little rough but wont bogg out, i haven't really had an opportunity to take her on the highway much so i have no idea on what kind of mpg i can expect im hoping $60 will cover gas for a 300 mile trip from houston to san antonio TX. any and all info or quick tips fast tune ups would be greatly appreciated. i can't wait to get to spend some time with this bike it seems like a ton of fun.

the mixture screws have nothing to do with sync. they have a big effect on idle. you need to get them out and blow out the passages then set them at 1.5 turns out from all the way in as a starting point.

when you take them out there should be a spring, washer and o-ring on each screw. If you dont see it, it's still stuck inside carb. make a tiny hook oout of small wire and pull them out, then blow out everythign and make sure it flows

Check carb holders for vacuum leaks.

hey i just realized you're working on a 2 stroke. Lucky bum! The H2 is one of my dream bikes. Anyway... Sounds like maybe you got it fixed, but if not, it could be a leak at the crank seal. Sucking in air and revving. Or worse - you may need to split the cases to fix the leak. I dunno how the bottom end goes together on those, but airleaks on the botom of an old 2 stroke is not uncommon. A shop could probably do a leak down test to tell you exactly.

idle adjustment...hmmm..seems you stumped the mechanics on here for months....

idle screw....hmmm....

Nelson wrote: hey i just realized you're working on a 2 stroke. Lucky bum! The H2 is one of my dream bikes. Anyway... Sounds like maybe you got it fixed, but if not, it could be a leak at the crank seal. Sucking in air and revving. Or worse - you may need to split the cases to fix the leak. I dunno how the bottom end goes together on those, but airleaks on the botom of an old 2 stroke is not uncommon. A shop could probably do a leak down test to tell you exactly.

Did they even make an 81 750 H2 in 1981? I thought they stopped the 750's in 1975 or 1976? I never heard of LTD H2's. So I think what he meant was a 81 KZ750 H LTD model four stroke. But I'm no expert, my knowledge is limited to the big early Z's and KZ's and limited in scope even with those models .

KZJOE900 wrote:

Nelson wrote: hey i just realized you're working on a 2 stroke. Lucky bum! The H2 is one of my dream bikes. Anyway... Sounds like maybe you got it fixed, but if not, it could be a leak at the crank seal. Sucking in air and revving. Or worse - you may need to split the cases to fix the leak. I dunno how the bottom end goes together on those, but airleaks on the botom of an old 2 stroke is not uncommon. A shop could probably do a leak down test to tell you exactly.

Did they even make an 81 750 H2 in 1981? I thought they stopped the 750's in 1975 or 1976? I never heard of LTD H2's. So I think what he meant was a 81 KZ750 H LTD model four stroke. But I'm no expert, my knowledge is limited to the big early Z's and KZ's and limited in scope even with those models .

its a four stroke, and usually a hanging idle is an overly lean or rich condition but if its hanging and staying its something else, i assume you checked the idle adjustment on the carb bank and any cable adjusters in line and on the throttle itself to make sure the throttle wheel is at rest at closed position, lmk and ill get back to you on the next thing id try if you have tried everything else. im also assuming you already syncronized the carbs.

EDIT: I see you already discovered the problem after combing your posts for details.