TOPIC:

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

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Good Fortune!

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.

Good Fortune!

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.

Good Fortune!

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.

Good Fortune!

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?

Good Fortune!

Long shot here but some car carbs are designed such that they bleed air into the system at low speed so the idle speed doesn't drop too fast because doing so leads to higher emissions than a slow drop to idle.

You may want to ping a Ninja message board to get confirmation about how the carbs are supposed to perform. It may be that the condition you mention is normal.

I notice Loudhvx and Tyrell Corp have not commented on this ..... these two know the 550s from front to back and they could maybe help you out..... Edit Whups never mind was going by what you have in your signature.

We talk about a zx900a1 (gpz900r), not 550.
To answer your question , :No is not normal for this bike to do this.
The rev counter its ok, you can barely hear the engine hanging.
Yes, the engine sometimes do that at higher rpm.
Yes if i blip the throttle she hangs above 1500 and then return to idle a bit slowly.( Or faster only if i put load using the clutch..)
The problem was present also with the old intake boots and before the carburetor overhaul. Its still here
Maybe a butterly shaft leak? I dont know if this is possible , since i cant find the leak in any way. I tried propane, wd40, carb cleaner. Nothing change.
I dont want to put a hole in a piston
i don't think it can be a electronic ignition trouble, since that become worse when it's warm. when cold it's running perfect.
a crack in the carburetors body? a crack between carburetor and one or more vacuum port? if so, why i can't find the leak using all the methods descripted above? ..

Like I stated earlier, spraying stuff on the carbs and boots is an unreliable way to find vacuum leaks. I've been through this a number of times on old UJM carbs, Suzuki GS bikes for example . Those bikes use an O-ring on the carb boots and they are almost sure to leak if they are the originals because the O-ring gets hard and shrinks. I've had this happen even after spraying stuff on the boots did not show an increase in idle speed.

You may want to try applying some heavy grease around the throttle shaft bushings to plug up any leaks that way. I'd check the choke's too since they work by allowing bleed air into the system and thereby increasing the idle speed from that.