81 KZ550 Throttle Hangiing before returning idle

OK, So my 550 ran pretty good last year. Only issue with it was being cold blooded and taking 20 minutes before it would idle on its own. Fast forward to this year. I just finished my GPZ conversion on the bike. Only thing I did to the engine was remove the emmisions from the valve cover and put the APE block offs on it. Went for a ride and throttle hangs between shifts. Tried adjusting carb and no luck. So now I put the old emissions plates on and still doing it. Pulled the carbs apart and made sure clean and good. Replaced the 32 pilots with 35's and drilled the mains from 92 to 96. Still doing it. I have replaced throttle cable with new and put on a nice light return spring. Carbs open and close great so not with that.

Anyone have any insight to what could be causing this all the sudden???

A hanging idle is usually cased by vacuum leaks and/or a lean condition. The rubber carb boots that attach to the head are prone to cracks, and if the airbox boots at the rear of the carbs are not fully sealed false air can enter the system that way too.

Where are the pilot screws set and did you vacuum sync the carbs?

BTW, spraying junk on the carbs/boots as a way to try to find vacuum leaks (as some people invariably always suggest) is an unreliable method unless the leaks are vary large.

Nessism wrote: A hanging idle is usually cased by vacuum leaks and/or a lean condition. The rubber carb boots that attach to the head are prone to cracks, and if the airbox boots at the rear of the carbs are not fully sealed false air can enter the system that way too.

Where are the pilot screws set and did you vacuum sync the carbs?

BTW, spraying junk on the carbs/boots as a way to try to find vacuum leaks (as some people invariably always suggest) is an unreliable method unless the leaks are vary large.

This all started before I even touched the carbs. It all started after I changed the exhaust and removed the emissions piping from the valve cover. All the carb stuff I did was after the fact and still having same issue.

Could the o-rings under the block off plates on the valve cover be leaking now causing the issue?

Air screws are 2 turns out. Running a 35 pilot and drilled out mains to 96.5. Air box is intact with boots etc. Intake boots were not touched and are nice and soft.

The air injection system used carb vacuum. Did you plug up the ports on the carbs that were feeding that system?

Sometimes those carb boots on the head seem soft but they leak regardless. Mostly where they bolt to the head.

You didn't mention vacuum sync. i'd open the pilot screw to 2.5 turns open and then vacuum sync.

Nessism wrote: The air injection system used carb vacuum. Did you plug up the ports on the carbs that were feeding that system?

Sometimes those carb boots on the head seem soft but they leak regardless. Mostly where they bolt to the head.

You didn't mention vacuum sync. i'd open the pilot screw to 2.5 turns open and then vacuum sync.

I am not sure of what ports on carbs you are talking about. The ports in the valve cover were connected together in a loop and nothing back to the carbs. There are 2 lines on the carbs that go to nowhere but were like that all last year without issue.

I did not vac sync carbs again after I had them off because I never touched the slides etc so figured they should still be in sync. I did sync them myself last year.

The air injection system air valve uses ported vacuum from the carbs. My point is to make sure you don't have any vacuum ports that are open now that the air injection system has been removed. I'm not super familiar with the TK carbs on those 550's so I can't offer anything more specific than that. Again though, a hanging idle is almost always related to a vacuum leak or a lean condition one way or another.

Nessism wrote: The air injection system air valve uses ported vacuum from the carbs. My point is to make sure you don't have any vacuum ports that are open now that the air injection system has been removed. I'm not super familiar with the TK carbs on those 550's so I can't offer anything more specific than that. Again though, a hanging idle is almost always related to a vacuum leak or a lean condition one way or another.

Sounds good. Thank you. I'll pull it all apart again and see what we got.