Idle screws

[snamelc]

I have a Series II with freshly re-built Zenith carbs. Both of these carbs have two idle screws, one on top and the other below the throttle shaft. My maintenance manual refers to one or the other but not both on the same unit. The only way I've been able to get the car to run is to screw the top ones all the way down shut. Am I missing something here or did some previous owner combine two carbs incorrectly, top from one and bottom from the other? It might help to know that I do not know the position of these screws before re-build and that the re-builder left them open. I suspect previous owner had them shut. Otherwise the carbs flooded constantly.

Bill

 

[RootesRacer]

I have a Series II with freshly re-built Zenith carbs. Both of these carbs have two idle screws, one on top and the other below the throttle shaft. My maintenance manual refers to one or the other but not both on the same unit. The only way I've been able to get the car to run is to screw the top ones all the way down shut. Am I missing something here or did some previous owner combine two carbs incorrectly, top from one and bottom from the other? It might help to know that I do not know the position of these screws before re-build and that the re-builder left them open. I suspect previous owner had them shut. Otherwise the carbs flooded constantly.

Bill

It sounds like someone might have mixed upper and lower carb parts to make one carb set. There really only should be one set of adjustments (only on the top, or only one the bottom).

 

[SIVAllan]

I have a Series II with freshly re-built Zenith carbs. Both of these carbs have two idle screws, one on top and the other below the throttle shaft. My maintenance manual refers to one or the other but not both on the same unit. The only way I've been able to get the car to run is to screw the top ones all the way down shut. Am I missing something here or did some previous owner combine two carbs incorrectly, top from one and bottom from the other? It might help to know that I do not know the position of these screws before re-build and that the re-builder left them open. I suspect previous owner had them shut. Otherwise the carbs flooded constantly.

Bill

Which model Zeniths? WIA or WIP?

For 36 W carbys:

For WIP-3 "Air regulating screw is fitted instead of volume control screw"

"In those carburetters having -3 in the type designation, i.e. 36 WIP-3, the mixture control for idling is an air regulating screw, mounted higher up the body of the carburetter, in fact in the floatchamber cover. The screw is cone ended with a spring to ensure it stays in the position to which it was set. Turning the screw varies the amount of air admitted and controls the depression acting on the slow-running jet. The action is the reverse of the volume control screw, and turning clockwise the air regulating screw enriches the mixture by increasing depression on the jet. Turning anti-clockwise weakens the mixture..."

"Idling is adjusted by means of the throttle control screw (at the bottom). If screwed in the screw will open the throttle wider and increase the engine revolutions..."

from Zenith service bulletin SB 201

To get started I am assuming:

Top screw in all the way--back out 1 1/2 turns...
Bottom screw out all the way--back in 1 1/2 turns...

Top screw is delicate be very cautious.

Any Zenith experts out there?

Allan

 

[snamelc]

The carbs are 36 WIP-3's according to the info stamped on the float chamber cover. Can the rest of the carb be from some other Zenith and still have the two parts mate?

Bill

 

[SIVAllan]

The carbs are 36 WIP-3's according to the info stamped on the float chamber cover. Can the rest of the carb be from some other Zenith and still have the two parts mate?

Bill

Bill, I can't answer that question. Maybe; maybe not .

Could you post a pic of the carbs?

It's not clear to me just what has happened to your carbs.

Also I am among the least knowledgeable of the folks here on carbs; I do have the same carbs as you do though, and have gotten to know them a little bit.

Allan

 

[Dr.NO 007]

Zenith Carbs.

Hey Guys
Hope these pictures are of some help to resolve your puzzle. I am not a mechanic nor am I a carb expert.... but I do have a Series II with twin zeniths on it and thought I would take some pics for you.
(I removed a support bracket from the front of the main throttle rod.)
Chuck
- if you want send me a pm with your email address and I will send the 3 pictures

SORRY !
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Please try again later.

 

[snamelc]

OK, I'm going to try to post a picture as an attachment (paper clip) showing my idle screws. I've removed the spring on the upper screw to allow it to seat all the way closed easier. If anyone has a setup like this, I need to know how you've handled it.

Bill

 

[snamelc]

OK, so the quality of that image stunk! Let's try again.

Bill

 

[RootesRacer]

OK, so the quality of that image stunk! Let's try again.

Bill

Once again, I'd say someone put the top from one type to the bottom of the other.

The top screw is an air control, the bottom is a fuel control, they do opposite things, and perhaps COULD work if the tops are set (perhaps closed), and never touched again.

 

[SIVAllan]

Bill,

A pic of a WIA type Zenith.

I'd listen to Rootes racer; better yet find an intact set if those won't cooperate.

Allan

 

[snamelc]

Great response, group! It looks like absolutely no one else out there, at least those who have followed this thread, has come across two idle screws on the same carburetor. It looks like the solution of shutting off the upper one works so I'm sticking with that.

Thanks for the support.

Bill