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FWIW [perhaps not very much ]

www.dansmc.com/cdiignition.htm

Good Fortune!

If you haven't already done so, try this -

Disconnect the throttle cables at the carbs. The start the bike and give it some revs by manipulating the throttle at the carbs using your hand. If the revs still hang you have ruled out the cables and throttle grip as a possible problem. If the revs still hang you have identified the problem which should be easy to correct by lubing the cables and throttle grip. Ed

Cable its ok and snap return as it should..

Can be a sticky valve problem?

shamal wrote: Can be a sticky valve problem?

Doubt it. Pretty sure it's a lean mixture or maybe spark at wrong time.

I have a GPX 750 cdi for spare. Can i use it?
I know the pinout its the same. I don't know
If will work.
Toughts?

Update.. right now i checked with the timing light idle ignition timing. Its perfect matched "F" with the crankcase mark.
I thighten more the boots , i dont want to bent them so i dont know if is good thightening too much.
Idle is still as above.. it drop to normal but just take a pair of second ..

shamal wrote: ...new carb diaphragm....

Perhaps one of the vacuum valve throttle slides might be ever-so-slightly hanging, for whatever reason, such as imperfect fitment of the replaced diaphragm or a speck of crud in one or more of the carbs that's interfering with immediate full down position seating/closure of the throttle slide upon closure of the throttle.

Am presupposing that all the vacuum valve springs and spring seats and jet needles and needle jets are all in perfect condition and are properly installed in what are believed to be immaculately clean carbs.

Good Fortune!

The carbs are clean. Trust me. Ultrasonic.
Jets the same.
I was thinking about that too, but when i close the gas, the butterflies are closed, so i think even if a slide valve can be slower than others when close , have this influence? I think not so much

FSM If needed:

Click here > www.dropbox.com/s/8g47k3pmjmoxc97/GPZ900R%20FSM%201990.pdf

Fuel System pages 2.7 - 2.8 cover sync and fuel levels.

Good Fortune!

Patton wrote: FSM If needed:

Click here > www.dropbox.com/s/8g47k3pmjmoxc97/GPZ900R%20FSM%201990.pdf

Fuel System pages 2.7 - 2.8 cover sync and fuel levels.

Good Fortune!

thanky you. fuel level its ok. one thing i have NEVER consider on ANY bike is the point at page 2-10. ''install the slide valve spring seat and turn the seat so that it doesn not block the hole in the bottom of the slide valve''
maybe i ever had fortune, but honeslty i think if this hole it's partially plugged by the spring seat, the carb will suffer when the gas is opened, or under load. maybe with a certain difficult at rising the slides, but i don't think this can affect the return to idle. or it can?
what you think?
the engine it's just running like a rocket...

Has the physical carb sync (i.e., equal butterfly closures) been verified with vacuum gauges?

Good Fortune!