facel6

there is still something wrong with my WCFB carburetors

i have the smoothest idle (and also the highest vacuum) with the idle mixture adjustment screws fully closed

I started my tuning with the screws opened 2 turns and measured very poor vacuum (about 10) at 850 rpm
Closing the screws 1/4 of turn makes me win about 100 rpm and 1/2 of vacuum
I can repeat the operation until the screws are fully closed. At the end, i have between 14 and 15 vacuum, which seems to be a correct value for a Duntov cam
Idle is smooth, but the engine is still running too rich.

I made another try
I screwed back the idle screw, so the throttles were fully closed. I opened the mixture screws 2 turns
when the car switched from fast idle to normal idle, the engine stopped instantly

Whats wrong here with my idle circuit and what can i do to improve it ?

tbarb

Usually the idle SPEED adjustment screw is set to where the transfer slot is just barely visible so at idle fuel is controlled by the emulsion screws. Try to set the idle speed screw about 3/4 to 1 turn and get the engine air from somewhere else, (secondary throttle blades, PCV valve etc.) and see if the emulsion screws set for best idle at approx 1 turn out.

Frankie the Fink

tbarb is correct. The discussion below assumes you to NOT have a vacuum leak.

But I'm not sure the OP knows what the transfer slot is so pic provided.

If you run the idle SPEED screw in far enough you OVEREXPOSE the transfer slot and the idle MIXTURE screws LOSE CONTROL over the air/fuel mixture. Hence, no effect when turning them or you can completely close them with no effect. You have 'chased' the best idle past the point of no return.

When this happens its best to go back to a baseline. Seat the MIXTURE screws LIGHTLY all the way in...then back out 1-1/2 turns.
Adjust the SPEED screw all the way out so its not touching the stop..then in until it touches the stop then ABOUT another 3-4 of turns in.

Start the car and WITHOUT touching the MIXTURE screws bring the car to curb idle with the SPEED screw (it may be running rough).

Start adjusting the MIXTURE screws for highest vacuum on the gauge alternating back and forth while keeping the idle speed at spec.

If you don't have a vacuum gauge, get one, take it to someone who does, or, else sell the car....that tells me you really don't want to properly tune the engine

Without a vacuum gauge you are tuning for highest, smoothest idle -- essentially "by ear". Few novices have that ability - they may think they do - they don't...

facel6

don't worry, Franky

i know what the transfer slot is. I know the theory of those carbs and have read the manual at least 2 dozen times

i think i followed scrupulously the procedure you mentioned with the result i described
Each time i screwed the mixture screws 1/4 in, the rpm and vacuum increased, so i needed to correct this by screwing out the speed screw to stabilize the idle at about 850 rpm
At the end of the procedure, mixture screws were fully closed and my idle speed screw was (only) open about 1 turn

tbarb

Be certain that at one turn on the idle speed screw the transfer slot is just barely visible. At that point if engine runs best with the emulsion screws all the way in then it's getting fuel from somewhere it's not supposed to. The purpose of the curb idle emulsion screws is to set/trim the IDLE A/F ratio, if the transfer slots are overexposed at idle large amounts of fuel will be drawn from there and the emulsion screws will have little effect, the engine will run rich.

facel6

i need to disassemble the carburetor to check this

plaidside

What is your base timing? If the base timing is too low then you will have to raise the idle with the throttle screw uncovering the transfer slot.
Did this condition just start, was there anything performed before this happened?
When I first installed my WCFB's the front two plugs were fouling and I had not mixture control.
Is this condition on both carburetors?
What I found is someone put two primary throttle plated in the secondary carburetor that was .030" larger and it would not allow the throttles to close enough. I changed the plates and it has run flawlessly since.
Joe

This is the throttle fully closed, transfer slot exposed:


This is with the correct plate:

facel6

OK

i just disassembled my carb.
The transfer slots are exposed like in the first picture in the previous post

facel6

Should the slot be barely visible from top or from underneath ?
I guess when looking from under, right ?

If so, the slot are fully exposed with the idle speed screw at one turn. They are even partially exposed when the idle speed screw is touching the stop (=> when throttle valves are supposed to be fully closed).

Frankie the Fink

A rule of thumb is that, with the throttle plates FULLY closed, the exposed transfer slot should appear square....looking in the throttle bores from underneath....this seems to be a good starting point for nearly all carbs...

I don't have a pic of a WCFB with transfer slots (oddly enough) but you get the idea... The idle SPEED screw controls the position of the throttle plates, not, the idle MIXTURE screws..

Picture #1 in Joe's post #7 clearly has an over-exposed transfer slot...

facel6

OK

so far, so good. I've understood this.
But in my case, when the throttle valves are fully closed, at least the half of the idle ports is exposed

What can i do to correct this ?

Frankie the Fink

Have you backed out the idle speed screw as I stated above ?
This is what controls how much of the slot is exposed ...

Its NOT an idle port - its a transfer slot - lets keep our nomenclature consistent please...

Frankie the Fink

Watch the video and note at the start that with the idle speed screw NOT touching the stop the transfer slots are almost completely covered by the throttle plate.

Set your throttle plates identically as how mine end up in the video...then lightly seat your mixture screws and then back out 1 to 1-1/2 turns and these should be good initial setting to start tuning.

If you can NOT get the transfer slots as I show them then you may have mismatched parts as Joe (plaidside) discusses in post #7 above...

facel6

yes, fo sure i've backed out the idle speed screw.

Frankie, i think what you're calling transfer slot is called idle port in the WCFB service manual. Isn't it ?






I definitively cannot get the transfer slots covered when the throttle valves are fully closed as you explained it.
I will try to post some pictures later ...

Frankie the Fink

Indeed sir, I stand corrected, and, learned something new. Great graphic BTW - you can see the interrelationship of the "idle port" and mixture screw -- they basically control the same passage. The idle port is a "coarse" adjustment and if the slot is over-exposed it negates any effect of the "fine" adjustment via the mixture screws.

I think "transfer slot" is more descriptive though as this opening transitions the carb from the idle circuit to the cruise circuit as the throttle plate opens

That is not right and you'll have to get to the bottom of that to get your carb straightened out

facel6

i could manage to get the throttle valves in the correct position while fully closed





Will make a new try ...

Frankie the Fink

You may want to record how many 'turns' in from just contacting the idle speed screw stop that is, so, with the carb ON the car you can get back there if you get messed up again!

BTW - you're gonna hate me for this but your throttle plate is not installed correctly.

The screws are too long and not properly peened over (staked). Look at the screws in the second picture in Joe's post #7 (plaidside) where he installed the new, correct throttle plate and look at the length of the screws and how the ends have been staked to ABSOLUTELY make sure the screws can not come loose and wind up in your engine.

Likewise look at the all original carb in my video and note the length and the staked over ends of the screws...you will clearly see this on the secondary plates near the end of the video as I zoom in.

Strongly suggest you fix that, or, take it to somebody who can!
I'd hate to see you dick up your motor through some rebuilder's incompetence

GTOguy

Those screws really jumped out at me, too. Please take Frank's advice here!

facel6

not at all. Thank you for the advise

I just made a new test. It's always the same. I obtain the most vacuum (about 14") with the idle adjusting needles fully turned in

Frankie the Fink

After seeing those throttle plate screws I'm wondering about the quality of the rebuild that may have been done on your carburetor. Turning the mixture screws in leans out the idle mixture indicating the carb must be running rich which makes little sense to me as your low vacuum at idle indicates you're sucking air somewhere (which would create a lean mixture). To wit, ...you have some weird **** going on...

It's be interesting to try a couple more things:

1) Check your ignition timing and make sure its to spec..

2) No jokes here please. Take that vacuum line to your vacuum advance and suck hard on it until you see it move to its farthest point and put your tongue over the end of the hose in your mouth to 'hold' the vacuum. The vacuum can should not 'leak down' and should hold the vacuum for at least 10 seconds. If not your vacuum advance is leaking (Of course, if you have a My-T-Vac to apply vacuum to the hose you can avoid the fellatio approach)

3) With the vacuum gauge "T"'ed back into the vacuum advance line -- cap off that power brake booster fitting with a rubber cap or else plug it; and see where the idle vacuum and mixture adjustments take you with this change...