sticking throttle,,

hi all, I have a 1980 kz1000 LTD, completely bone stock, I am having an issue with the carbs,, above 3000 rpm the throttle sticks open, like having cruise control, I thought it might have been the cables, but if i shut the bike off and restart, the bike is at idle. U can even see the throttle snap closed when u shut the key off, so is the passage of air through the carbs holding them open? and how do i fix it?

Put some slack in those throttle cables. The carbs are mechanical so either the cables lack slack or the slides are not shutting as they should. You may also have the phillips head screws in the carb holders catching on something slightly as the bellcrank rotates open. You may have a filthy throttle that hasn't been lubed since the bike rolled out of the factory.... There are a other things that can cause this issue but since we got no history, I would prefer not to go over every possible issue. Did the bike EVER operate as it should and then this problem just start out of the blue?

Hi sorry for the slow reply,,I have owned the bike for 4 yrs. now, and the carbs have always stuck, the cables on the bike feel no different than the brand new OE cables i bought to replace them. The Carbs were removed over the winter,proffesionally torn down, cleaned, some "o" rings and gaskets were replaced. Better performance but the throttle still sticks above 3,000 rpm.If I hit the kill switch with the bike running at over 3,000 rpm the throttle shuts imediately. throttle spring seems to be very strong,, i dont understand why its not closing the throttle.I dont see any mechanical interference with the throttle.

Well, when my company disassembles carburetors, we fix problems like the one you describe. I would take the carburetors back to where you got them "professionally torn down" and give them a chance to fix the problem. Good luck with your problem.

I would rather know what the problem is than start looking to assign blame,they stuck before they were torn down and continue to stick now,,

Most LIKELY you have an air leak (vacuum). A carb hose has come off or is missing or a vacuum line has a crack in it.

Check EVERY vacuum line. Check any rubber plugs on the carbs to see if they are cracked.

Bob

What you've described is a very strange problem indeed.

Are you saying that, when riding on the road, you can just let off your throttle and the bike keeps on keeping on at the same speed? Would this occur indefinately? Can you force the throttle shut by rotating the throttle away from you? Can you get the motor to slow back down by "wiggling" the throttle?

If my understanding is correct I don't think that its an air leak.

I don't think that the "passage of air", as you put it, is causing your throttle to stick open. If your throttle is indeed staying open, it much more likely that is is do to some frictional problems or a bad connection between carburetors.

Let us know what you find.

yup, its just like having cruise control,,i have the cables real loose right now, not that it made any difference. With the bike parked i can rev the engine over 3k and it will stay there, if i use the kill switch to shut it down and then restart it, without touching the throttle at all it will be at idle.freaking wierd,,,

exactly what carbs do you have on the bike ?

Does it have a smog valve on it? Mine had one and when I got rid of it the motor ran alot better.

I still think its a vacuum leak issue. Your carbs are sucking air in somewhere they are not supposed to.

It's amazing how many guys are rebuilding thier carbs and then suddenly have idle issues.

I did the same thing. After rebuild the motor seemed to have a mind of its own. If I cranked it to 3000 rpm it stayed there. It was like cruise control. I rebuilt the carbs about three times trying to figure it out.

I found two errors I made. One: there is a hose nipples between carbs 1 and 2 and also between 3 and 4. I thougt they were vacuum connections and plugged them. Turned out they were bowl vents.

two: I had the idle screw set too high appently. Because when I set the idle to about 700 rpm (or less) the high idle problem went away. And yes, it will idle that low. I also made sure the cables had slack.

That seems to have fixed my idle problem. Maybe it will help some of you out.

The fact that the problem started after a carb "rebuild" is a clue that you created the problem yourself (like me).

Also,it's an old bike....something could have worn out.

Bob

Post edited by: Bob_79KZ, at: 2007/07/24 22:26

the stock mikunis, nothing has been changed on the bike, i am not sure of the model,, vm28 maybe? bike is a 1980 kz1000 LTD B4, completely stock, i can trace the bike all the way back to the salesman that sold it new in 1980 it is as original as the day it was delivered.

Yep, VM28SS's. I can track my 79 KZ back to the original sale too. So its box stock, like yours.

Try lowering the idle stop a little...then readjust the air bleed screws...then lower the idle a little more...then re-adjust the air bleed (idle mixture) screws again.

I did that about 3 or 4 times and now the bike idles good and does not stick at high rpm's any more. I idle at about 700 rpms. It used to idle at about 1100 rpm's when I was having all the problems with it.

I guess too high of an idle setting cause's strange problems.

Good luck and don't give up,
Bob