Zenith Carb issue
 

Hey guys question of the day LOL. I got my ‘30 Tudor fired up after setting the timing. We cleaned and rebuilt the carb. Everything looked good float level and such. Started the car it would only run for 30 seconds or so then stall. I realized I forgot to open the fuel mix on the choke rod. After that started right up but I cannot get it to idle. The idle adjustment will back all the way out and all in without any changes in motor performance. Also she will back fire a bit if I throttle up and let off. I tried adjusting the fuel mix about a quarter turn or so but nothing seems to help. Any suggestions?

Re: Zenith Carb issue
 

Backfiring is usually a sign that the mixture is too lean.

Make sure the throttle linkage is not prohibiting the throttle plate from closing all the way. If you still have problems then there is something amiss in the carburetor or intake manifold. Look for air leaks like at the throttle shaft. It is possible that a foreign object has gotten into one of the jets. You may have jarred some particle loose in the pipe or elsewhere.

This site may help: https://model-a.org/default.html

Re: Zenith Carb issue
 

the first thing i would do is check the flow of fuel at the fuel line into the carb. make sure there is good flow to the carb.
if so then make sure fuel is filling the float bowl. is the float valve working properly.

as above backfire through the carb is usually too lean.

if you have lots of fuel entering the float bowl then its time to take that carb apart again .

Re: Zenith Carb issue
 

How was the carburetor cleaned/rebuilt ? All the passages need to be cleaned with a good cleaner and blown clear and dry. The throttle plate needs to be sitting properly in its bore. Then the the adjustments need to be made.

Re: Zenith Carb issue
 

Last time I had an issue where the idle adjustment did not make any changes no matter what the position it was a blown head gasket. So, if you can't find any vacuum leaks which can also cause that same symptom do a compression test on all the cylinders. It simple and tells a lot about the engines health.

Re: Zenith Carb issue
 

Carb was soaked and cleaned/Blown out but I did take the throttle plate off more then once I will definitely check that out along with all the other suggestions. Thanks all!!

Re: Zenith Carb issue
 

if the air/fuel idle screw does not change the way it runs at an idle.
you have to pull it apart again and clean all the jets, all the passages, the well that the low jet sits in. it has to come out and be cleaned as well as below that well there is passages.
there are lots of tiny holes that need to be clear. take your time look close. check that you have the rite gasket/washers on the jets that are supposed to have them. rushing through the carb cleaning doesnt work.
you probably don't have to take the throttle plate off.

Re: Zenith Carb issue
 

When you cleaned and blew it out it did you remove all of the jets, GAV adjusting needle assembly and seat etc...?

Re: Zenith Carb issue
 

I had an issue where the shaft from the steering column to the throttle linkage was too long, and it would not let the throttle plate close completely. Hence the idle adjustment screw at the carburetor didn't work. I had to remove the shaft, cut about 3/16" out, rethread the two ends and use a coupler and jam nuts to adjust the shaft. Problem solved.

You can test to see if this is your issue by disconnecting the arm from the throttle linkage and see if you can adjust the idle speed.

Tom Endy wrote an excellent article on cleaning the Zenith passageways, see it at http://www.santaanitaas.org/wp-conte...p-Oct-2011.pdf.

JayJay

Re: Zenith Carb issue
 

I have a flying V shape in my rod for the same reason.

Re: Zenith Carb issue
 

If the throttle plate isn't closing all the way the idle mixture screw will have no effect on how it runs.

Re: Zenith Carb issue
 

I have a bend on mine. A long time ago I tried to replace it with a new one and it kept popping off. I put the old bent one back on and all is good.

Re: Zenith Carb issue
 

I had a 'start and run for a few seconds' problem too. I had cleaned the passages thoroughly, measured and cleared the jets and reinstalled themwith little red gaskets. I eventually discovered that the main and/or cap jets were leaking at their base. I had to switch to Bratton's carb kit to get the little black washers. The leaking stopped.


When the car has set for several hours, it should be dry in the intake/air horn at the base of the two jets in the venturi. (main and cap) Stick your middle finger in there and feel for gas at the base of the jets. I could stick a dry finger in and touch only the upper part of the jets and they were dry at the top. I split the carb again and set the bottom on the bench and filled it with fuel. The jets were leaking at their base.

Re: Zenith Carb issue
 

Ivan - your engine compartment looks a lot cleaner than mine (which is unrestored), I'm jealous!

JayJay