Model A Runs rich after Carb rebuild

[wadeyboy]

Only a Junior here however i have just got my 29 Tudor running after sitting in shed for some ten years or so. i refitted my marvel as well. However when i started her she was running real rich. I have since found out I had two minor problems the choke control lever was coming out of the GAV screw groove plus was not opening far enough this was because other end of lever was hitting steering shaft housing. these have been fixed with a small adjustment.
Do i have a problem now as my sparkplugs were coated with soot and i have taken them out to clean up but inspecting the plug holes its pretty black in there as well?
Or will this clean itself with better fuel mix?

[Y-Blockhead]

Originally Posted by wadeyboy

Only a Junior here however i have just got my 29 Tudor running after sitting in shed for some ten years or so. i refitted my marvel as well. However when i started her she was running real rich. I have since found out I had two minor problems the choke control lever was coming out of the GAV screw groove plus was not opening far enough this was because other end of lever was hitting steering shaft housing. these have been fixed with a small adjustment.
Do i have a problem now as my sparkplugs were coated with soot and i have taken them out to clean up but inspecting the plug holes its pretty black in there as well?
Or will this clean itself with better fuel mix?

I say drive her. Remember on a Marvel the idle mixture screw is opposite a Zenith or Tillotsen. It adjusts gas not air, so turning it out enrichens the idle mixture.

[Big hammer]

Originally Posted by wadeyboy

Only a Junior here however i have just got my 29 Tudor running after sitting in shed for some ten years or so. i refitted my marvel as well. However when i started her she was running real rich. I have since found out I had two minor problems the choke control lever was coming out of the GAV screw groove plus was not opening far enough this was because other end of lever was hitting steering shaft housing. these have been fixed with a small adjustment.
Do i have a problem now as my sparkplugs were coated with soot and i have taken them out to clean up but inspecting the plug holes its pretty black in there as well?
Or will this clean itself with better fuel mix?

Get her nice and warm , at a fast idle spray water into the carburetor, steam cleaning the combustion chamber and exhaust

[jeepguy1948]

I can’t say enough good things about David Renner. He makes what he sells and he flow tests every one before he sends them out.

[Alwaysamopar74]

Kinda on the same subject. Is there a way to tell if the jets are old original ones? I mean some of these carbs have been rebuilt a lot.

[Brentwood Bob]

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A little research will help you clarify the originals, and the nuisances of the carburetor rebuilding process. Rex Reheis, Tom Endy are two Good experts I would recommend.

[Ray in La Mesa]

Alwaysamopar74:
Original jets had numbers stamped on their bases and concave tips to preclude wicking & creating a leak.
compensator jet #18,19
cap jet #18,19,20,21
idle jet #11
main jet #18, 20

[Ed in Maine]

Any new jets purchased for a Zenith carburetor rebuild must be flow tested. If you don't, you will be wasting your time on the rebuild. Most jets are oversized. If you want to have a light grey tail pipe and good running, you need to size the Main Jet for 152 - 155 ml/min. The published range is 150 to 160 ml/min. If you use a Main Jet of 156-160 ml/min. you will have black carbon on your plugs and tail pipe. you will also find that the GAV is nearly closed for good running. You don't need extra gas, it is all coming through the Main Jet! Be sure your Compensator is sized 138-142 ml/min. Over the course of many Zenith rebuilds I experimented with Main and Compensator jet sizing. I have noticed that when the Main Jet is sized 150-152 ml/min. you might get a slight puff back fire when you lift your foot off the gas, your engine is going lean! You will get the best running economy. I have read that the published data for the sum of gas flows for the compensator and the Main Jet is about 295 ml/min. The published data for the Cap Jet is 160-185 ml/min. The sizing for the Cap Jet isn't as important. It is just a Jet to introduce additional gas from the GAV which is a variable.

One additional comment on jet sizing, the Zenith Carb has a nasty tendency to make the car stall when approaching stop signs. In my opinion, the Zenith design has a design flaw. The float is hinged at the rear instead of on the side as in other carbs. When your car is stopping, the gas flows forward uncovering the Compensator Jet and the float rises shutting off gas flow into the bowl further complicating things. The Idle Jet is momentarily starved. It is just the way things are and there isn't much you can do about it! The bottom line is that you must flow test to get optimum conditions inside the Zenith Carburetor. Good luck, Ed