TOPIC:

The opening of the number 2 butterfly its preset. Direct connected with the idle knob.
So with a 0.5mm feeler gauge. I set the number 2 butterfly to 0.5, then the same on the number 1 carb.
The same with number 3 and 4.
After that i vaccum synched the carbs like the manual above say.
The only thing i dont understand is the low reading. Something about 15mm Hg.
This can be late valve timing, and im fairly sure it is not the issue.
Or mybe late ignition timing. And this is possibile.
I bought a cheap used good igniter . I will try.
Today, i checked the gap of the pulsing pickup coils, and i found they were a bit too wide in air gap

Manual say to set 0.5 / 0,9
Since the 1.0 mm feeler gauge was free to move, i set them to 0.65.
Had No time to start annd try, but i think a too wide pickup air gap can result in retarded ignition timing.
This ignition , if im not wrong is a darlington power transistor and its not digital, but analogic. This mean there is no processor, but the advance in timing is calculated with a system of resistors and condenser.
If a condenser start going bad, and they Do, the advance curve is working fancy.
.

Hello shamal

I do some brainstorming or just an idea, but it could be a near solution for your problem.
Try to sync your carbs ( butterflies )mechanically to the same gap in the intake port of the carb bore with a feeler gauge or a thin wire.
Vacuum sync the carbs with a vacuum leak will lead you to the wrong direction.
You can check your actual vacuum sync with the feeler gauge for equal values.
If you on one carb a lot away from the others, then this is the carb that cause your problem.

Michael

EDIT: ignore my reply, you got the same thoughts as i was interrupt by girly

Maybe its time to leave the carbs alone and look elsewhere for the problem. I know youve considered the ignition but have you totally eliminated it? With all the time and effort youve spent on the carbs, it might be worth going through it. Take nothing for granted. Clean,inspect,replace. Top to bottom. You never know,you know!
My tuppence worth. Good luck with it.

To be honest i dont know what else i can look in the carburetors..

+1 on the manual bench synch before vacuum gauges, I still think this is an air leak issue. Had this problem before.

Check the pilot airscrew and o rings, which can cause similar problems, I have even seen a hairline crack here on a carb body casting before.

Any wear / bend on your carb needles? Carbs do wear out and I think this is an air leak. Do all the slides move up and down smoothly? They should all snap down sharply against the return spring pressure.

The thickness of the hose clamps is important, any thicker than stock and it has the effect of the boots squeezing the carbs off.

The outer O rings in the groove that goes into the intake rubber boots often get forgotten.

I had to retighten my intake rubber boots mounting bolts and use some sealant.

Could you try pulling a plug lead one at a time and try to isolate which if any cylinder makes the most difference?

I think incorrect valve timing or defective ignition module is unlikely to cause this hanging idle.

A bt of wear i think it is in the slide valves. At idle, when the vacuum pressure is higher , i ca hear a bit of clicking sound from the carbs due to the slides touching the carburetor bore. But they are free and smooth. And the diaohragm are new.
New also oring seat and springs in the mix screws. And intake boots, and manifold. And air filter.

ok i had some slepless nights: i keep thinking about cv carburetors and this is what i think . (apologize for my poor english.)
if we have NO vacuum leaks, a hang idle can be not LEAN , but RICH:
in a cv carburetors, when we set the mixture screw too far out, after drilling the EPA caps etc etc, the idle mixture become richer. So, to compensate this we need to open more the butterflies valves using the idle control knob.
when the butterflies of a CV carburetor are CLOSED, the vacuum in the bore is HIGHER. this push fuel off from the pilot circuit tiny hole, but if we keep trying compensate this ''too fuel'' condition by rising the idle with the knob...then the the carb start using the transition holes (3 tiny discharge ports just behind the butterflies) and the engine will hang because it is just NOT at idle, but it's just OFF idle....
your thoughts please.

if i set the screw 1/2 or 1/ 1/2 or 2 1/2 or more this seems have NO effect...

Does this mean that turning the pilot adjustment screws from 1/2 - 2 1/2 produces no change in rpm?

Exactly. No change. If i put the screws all the way in stalls. Otherwise no change


In the initial bench sync, the carb butterflies are supposed to be only barely cracked open an equal amount. If at this stage the equal cracks are too large, the later running sync may likely be with the equal cracks still being too large, which disallows proper metering by the pilot screw (being due to the butterflies being too far open and allowing mixture through the other orifices in addition to mixture allowed via the pilot screw adjustment). All of which could result in the reported non-effectiveness of pilot screw adjustments.

An aside -- Hopefully, the fixed/integrated/non-removable pilot air jets have never been "drilled out."

Good Fortune!

thank you, it's makes sense but maybe im fool. if the butterflies are supposed to moving togheter when i use the idle knob.. really matter how much opened they are during bench sync?
i think i can put them to, i don't know... 1 mm and then back the idle knob until they are closed.
i think im missing a step.
anyway, i used a 0.5 mm feeler gauge.
in the manual i can't find any info about bench sync. it just say '' inspect if they are the same''

A video showing the condition would be useful. Set the pilot screws to 3 turns open first. I still wonder if there is a controlled air bleed feature on those carbs for emissions reasons.

shamal wrote: thank you, it's makes sense but maybe im fool. if the butterflies are supposed to moving togheter when i use the idle knob.. really matter how much opened they are during bench sync?
i think i can put them to, i don't know... 1 mm and then back the idle knob until they are closed.
i think im missing a step.
anyway, i used a 0.5 mm feeler gauge.
in the manual i can't find any info about bench sync. it just say '' inspect if they are the same''

I might be wrong, but am thinking that the idle knob is supposed to be screwed way out to a non-functioning position while the initial equalization of the butterflies is being done.

I might also be wrong, but am also thinking that the initial equalization of the butterflies sets the maximum closed position of the butterflies, and that the butterflies aren't supposed to close any further regardless of how far the idle knob is screwed out later on.

Good Fortune!

Thank you. I think you are right. I pulled out the carbs again. I screwed the idle knob out to achieve no contact on the shaft.
Then i did again the sync on the bench.
When the shaft is released ,NO light pass from the butterflies, they are all the way closed. All the transition holes are clogged from the butterflies.
Now, if i slowly turn the idle up by opening the butterflies they are, at least visually, opening the same amount.
By the way, hell!!! The transition holes are very very very close to te butterflies..
Now im absolutely sure the only thing that work when the gas is released are the pilot screw holes.
I checked again the mix screws washers orings and springs, and reset again 2 1/2 turns out from totally closed position. As manual says.
So, in total absence of an air leak, what i should expect? ..