High RPM issue

Hi recently acquired GPZ 550 has the common High RPM problem I have read all the material that is available and run the vacuum test (sprayed with the break cleaner) and bingo second booth was leaking air I thought problem solved I bought all new booths, cleaned the carbs ultrasonically while they were out, put back all together and back to square 1, it runs a bit nicely once warmed up and with slight throttle turn the RPM goes to 3500-4000 and stays there for quite a while and sometimes I have to start adjusting the idle screw to bring it down, any ideas what else could cause that , also I have some "knocking and a bit of grinding noise coming from where clutch is" the bike work and drives fine clutch works gear are changing no problem
Any help would be appreciated
Paul

I had the same issue and turns out my butterfly valves were upside down! The cause of this? Well to be honest it was my expert carb cleaning and reassembly job. Since my bikes valves were not symmetric the pilot bypass circuit never closed. Once revved up the increased vacuum could generate enough force to really use that circuit.

But in all seriousness it could be a number of things.

Are your pilot jets turned in to factory settings or are they leaking air (check gaskets)?
Are there still any leaks present?
Do the butterfly valves close over the pilot bypass circuit?
Is your timing advance working properly and snapping back under spring tension?
Could your throttle cables be binding or not adjusted properly?

What gave it away for me, I basically pulled up a chair and six pack and sat next to the bike for an hour messing around with it. I finally found that I could press down (to close) the butterfly valve linkage to bring down the RPM. This pointed me to the carb/butterfly valve assembly.

I now run my bike with the idle completely out, if I turn it in any I run into a high rpm problem by exposing vacuum to my pilot bypass circuit (upside down butterfly valves did something similar). My pilot bypass circuit is seen as 3 little holes on the top of the carb, yours might vary.

Good luck sir!

Thank You for Your time answering this issue and Your experience with it
I didn't take the butterflies valves off for cleaning I just adjusted them open for ultrasonic cleaning , so unless someone before me took them off they should be OK they have numbers stamped on them and they are in right up position when I hold the carbs with diaphragm up
How do You check pilot jets?
from the air side I cant see the small holes butterflies cover them
Timing advance looks OK everything moves freely
I check the cable multiple times it has nice spring back to zero position on the throttle and at the carb level where is attached
I'm a second owner and not sure what a first guy did to the bike but when I bought it it already had that issue I simply thought that is basically vacuum leak since it responded to break cleaner test around boots that were old and stiff
Paul

In my experience, 9 times out of 10, the high RPM idle problems common on any old bike is caused by intake vacuum leaks caused by decaying rubber carburetor manifolds, hoses, or plugs. Occasionally I've run into carbs with worn out throttle shafts and carb bodies (on Mikuni BS34's). It is impossible to properly tune / set a carburetor with a vacuum leak.

The other 1 in 10 were problems in the idle circuits caused by dirt and / or dried up old fuel - usually plugged air / fuel passages and / or pilot / slow jets.

Wpala wrote: Hi recently acquired GPZ 550 has the common High RPM problem I have read all the material that is available and run the vacuum test (sprayed with the break cleaner) and bingo second booth was leaking air I thought problem solved I bought all new booths, cleaned the carbs ultrasonically while they were out, put back all together and back to square 1, it runs a bit nicely once warmed up and with slight throttle turn the RPM goes to 3500-4000 and stays there for quite a while and sometimes I have to start adjusting the idle screw to bring it down, any ideas what else could cause that , also I have some "knocking and a bit of grinding noise coming from where clutch is" the bike work and drives fine clutch works gear are changing no problem
Any help would be appreciated
Paul

The knocking sound is likely the primary chain bouncing / rattling around at idle - it should mostly go away when the carbs are sorted out and synchronized (balanced) properly and the idle speed set at the factory recommended RPM....

How do I know if my butterflies are upside down? maybe the person before me did that and that is what is causing all the problems

Paul