Problem with Rebuilt Carburetor

shew01

shew01

Well-known member
I'm missing something.

I swapped in a rebuilt carburetor just before driving to the Asheville MARC event, and the rebuilt carburetor worked fine for about 250 miles, i.e., until I arrived in Asheville. However, after I got to Asheville, the idle stopped working properly. I could not maintain an idle at anything lower than 1000 RPM (according to my tachometer), and I have fought this issue ever since. After I got home, the situation grew worse. The spark plugs fouled quickly (within a couple of miles after being cleaned), and the car had no power under load.

To isolate the problem, I swapped out the following with presumably good (mostly new) parts, with performance testing after each

- Coil
- Distributor
- Distributor cap
- Rotor
- Points
- Condenser

I cleaned and regapped the sparkplugs. I reset the points. I reset the timing with a Nu-Rex wrench (multiple times). I disconnected the tachometer (which takes its power from the coil.) I did all of this while leaving the rebuilt carburetor installed. Nothing I did improved the situation.

However, this afternoon, I swapped out the rebuilt carburetor with my original old carburetor, and the car's performance immediately improved. It's not perfect, but at least it's drivable again.

What am I missing? What could cause an issue like this when the car ran fine for 250 miles on the rebuilt carburetor? (I wouldn't think rust in the gas would be the problem because I replaced the fuel lines, fuel shutoff valve, and added a fuel shutoff valve pencil filter at the same time I replaced the old carburetor with the rebuilt carburetor.)
 
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No I haven’t. I’m a newbie with carburetors. That’s why I paid someone to rebuild it. I thought I’d post on this forum before contacting the rebuilder. Maybe it’s something dumb that I did.


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I would stop paying someone to look at your carb and try it yourself. It really is not that bad a project.

It realy sounds like something may have clogged a jet.

Do you have a firewall screen and a pencil screen in your tank?
 
I would drop the bottom of the carb and see if there is any rust in the bowl. I have had rust clog things after a lot less than 250 miles even with a pencil filter in place.
 
old31 said:
I would stop paying someone to look at your carb and try it yourself. It really is not that bad a project.

It realy sounds like something may have clogged a jet.

Do you have a firewall screen and a pencil screen in your tank?
Click to expand...


Yes, I have both.


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midgetracer said:
I would drop the bottom of the carb and see if there is any rust in the bowl. I have had rust clog things after a lot less than 250 miles even with a pencil filter in place.
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Ugh! It could be rust. I cleaned out the sediment bowl when I changed out the fuel lines. Now, it looks like some granules in the sediment bowl.

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I forgot to mention that the float valve leaked last night when I
58575315765bd74169feb110fad23d80.jpg

forgot to turn off the shutoff valve.


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The sediment bowl and float bowl don’t look that dirty to me. My sediment bowl will have rust particles in it immediately after cleaning and refilling it so I doubt that’s your problem. I’d still blow out all the passages. How much fuel did the float let leak out? Maybe it’s letting the fuel level get too high and that’s what’s fouling your plugs.
 
Thodge said:
The sediment bowl and float bowl don’t look that dirty to me. My sediment bowl will have rust particles in it immediately after cleaning and refilling it so I doubt that’s your problem. I’d still blow out all the passages. How much fuel did the float let leak out? Maybe it’s letting the fuel level get too high and that’s what’s fouling your plugs.
Click to expand...


It was a mess all over the floor under the car. The vapor smell was strong. I’m guessing at least several ounces of gas leaked out.


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Well that’s not good. At least it wasn’t a whole tank full on the floor. Maybe try swapping the float valve out of your other carburetor and see if that fixes it. Or did the float valve loosen up a little?
 
Check jets for tightness, had one loosen up shortly after repair, car ran but not too well , check the drilled passages in carb body, rust likes to accumulate in them also . Good luck.
 
Likely something simple. You are on the right track. Have one of the guys from your local Model-A chapter come over and help you a bit. I bet the two (or three) of you solve it in a short amount of time.
 
I agree with gdmn852, I wonder if something came loose, a jet, a bad float. Sounds like the car started running very reach and that affected performance and spark plug.
 
Any chance that you added an air filter while you were there? Assuming that an air filter is not the problem then it’s zenith gremlins. I no longer trust Zenith or any other rebuilt Carbuerator that I did not rebuild myself. Get some books, read up, buy some tools like a float level sight tube. Sometimes it comes down to parking your car next to your car, take the carb of the good car, turn around and install the good carb on your car, test it, put your carb on the good car and test it. Many will disagree with me but in my opinion, if you cannot work on your own Zenith Carbuerator you will forever be dealing with issues.
 
Seems to me if the car won't idle below 1000rpm, the problem is a plugged (with rust?) idle jet. Remove the jet, blow it clear or use a very small drill (#75) to clear it. This happens to all of us who have rust in their gas tank. LRF
 
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