TOPIC:

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.

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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.

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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?

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At about the 5 minute mark, this video addresses testing full closure of the slide.

Click here >

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Thank you. The only thing i havent noticed during carb rebuild is the fact about the hole in the slides.
Do you think if one or more of those are plugged by the seat ,the return at idle can be affected? Honestly i think this is impossible, since when you shut the gas off the closing of the slides are only spring operated. Or at least i believe!!!
Tomorrow im going to check if the 4 holes are not plugged by the springs seats. But i think this cant be a issue when you shut off the gas.
Carb are synched, bench and vacuum.
New boots front and rear
All moves smooth
New coils ,spark plugs caps ,wires as i mentioned above.
No leaks, as i can see by testing with propane and carb cleaner spray.
Mix screw default, or out, or in. Does not change the slow dropping idle.

If it's a given that all the slides are quickly going fully down upon closure of the throttle, would suspect that the temporarily racing idle would be caused by either a very minor air leak or an imperfect sync.

Perhaps double-check integrity of the vacuum nipple plugs/caps.

And double-check integrity of the vacuum hose from carb to petcock to assure leak free connections at carb and at petcock, and no cracks or tears in the hose.

I suppose it might be possible to have an internal malfunction in the petcock that's allowing an ever-so-slight air leakage from within the petcock into the vacuum hose.

Could test run with petcock on PRIme and putting a plug/cap also on the carb nipple that usually provides vacuum to the petcock. This should rule out the possibility of an air leak associated with the vacuum between carb and petcock.

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The bike does the same issue even in prime position. In any case the fuel tap and all the rubbers, lines, plugs are new .
I just noticed the problem almost disappear when engine is cold. Warmer it become, the worse.
What can be that start leak when engine is warm?

Would add 4th vacuum plug and test run with petcock on PRIme position.

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shamal wrote: ...
I just noticed the problem almost disappear when engine is cold. Warmer it become, the worse....

Not an unusual result in event of an air leak or sync issue.

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Blanked the second vacuum plug to te tap. Still the same.
I checked again the carbs. I mounted as per manual the diaphragm spring seat . I had 2 of 4 seats on the vacuum holes in the slides.
Checked again everything. Bench sync again.
Vacuum synch are showing 16cm hg in all 4 carb.
Idle 1000 rpm.
I test the gas cable. Snap return again.
As i rev the engine it respond well.
When i shut the gas off the idle return with a second of pause hanging at 1500 rpm, Then it drop.
Im so lost i was thinking switch to keihin cr special.
Engine starts really well with choke when cold and instantly with No choke when warm.
help

If test set the idle at 1500, and then blip throttle, is there any pause at a higher rpm before returning to 1500 rpm?
In other words, do the symptoms repeat with idle set at 1500 rpm?

Any doubt about accuracy of the tach?

Did the reported condition exist before the carb work was done?

Was the bike returning perfectly to idle at some point in the recent past?

When did the reported condition arise -- as in out-of-the-blue; or was there an ostensible reason such as first noticed after a period of long term storage?

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