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03-02-2024, 08:32 PM | #21 |
Junior Member
Join Date: Oct 2017
Location: auckland,New Zealand
Posts: 7
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Re: Model A Runs rich after Carb rebuild
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? |
03-02-2024, 08:46 PM | #22 | |
Senior Member
Join Date: Jul 2011
Location: Redondo Beach, CA
Posts: 5,915
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Re: Model A Runs rich after Carb rebuild
Quote:
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03-02-2024, 09:14 PM | #23 | |
Senior Member
Join Date: Jun 2014
Location: Land of Lincoln
Posts: 3,167
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Re: Model A Runs rich after Carb rebuild
Quote:
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Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done |
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03-02-2024, 10:07 PM | #24 |
Senior Member
Join Date: Jan 2022
Posts: 756
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Re: Model A Runs rich after Carb rebuild
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.
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03-04-2024, 03:35 PM | #25 |
Junior Member
Join Date: Apr 2022
Posts: 18
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Re: Model A Runs rich after Carb rebuild
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.
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03-04-2024, 04:53 PM | #26 |
Senior Member
Join Date: May 2010
Location: brentwood, ca
Posts: 4,301
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Re: Model A Runs rich after Carb rebuild
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03-05-2024, 07:52 PM | #27 |
Senior Member
Join Date: May 2010
Location: La Mesa Ca
Posts: 1,173
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Re: Model A Runs rich after Carb rebuild
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 |
03-07-2024, 01:36 PM | #28 |
Senior Member
Join Date: May 2010
Location: Washington Cty., ME or Flagler Cty., FL
Posts: 1,121
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Re: Model A Runs rich after Carb rebuild
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 |
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