|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
11-28-2022, 10:39 AM | #1 |
Senior Member
Join Date: Sep 2022
Location: Canton, Michigan
Posts: 118
|
Model A Runs rich after Carb rebuild
I recently rebuilt the carb on my '29 Fordor and now it appears to run real rich and sounds like it is missing. I put all the jets back where they belong. The one odd thing was with the rebuild kit from Synders, the gasket that goes between the 2 halves of the carb the side that has the venturi was a little smaller than what the original was. I did not take out the venturi when i cleaned it. Ideas on why it would be doing this? It also appears to surge at times and I can't keep a smooth idle when parked and or driving her.
Thanks everyone! |
11-28-2022, 11:07 AM | #2 |
Senior Member
Join Date: Apr 2021
Location: Central Illinois
Posts: 496
|
Re: Model A Runs rich after Carb rebuild
A rebuild of the carb without removing the venturi???? More info needed here. How was the car running before you disassembled the carb? etc.
__________________
"It ain't what you know for certain that gets ya in trouble. It's what ya know for certain that just ain't so!" |
Sponsored Links (Register now to hide all advertisements) |
|
11-28-2022, 11:09 AM | #3 |
Senior Member
Join Date: Sep 2022
Location: Canton, Michigan
Posts: 118
|
Re: Model A Runs rich after Carb rebuild
Car was running smooth, albeit a little rough.
|
11-28-2022, 11:14 AM | #4 |
Senior Member
Join Date: Jul 2011
Location: Redondo Beach, CA
Posts: 5,849
|
Re: Model A Runs rich after Carb rebuild
I was just reading an great article by Lynn Sondenaa in the March/April 2022 issue of the Restorer magazine on Zenith Carburetors (Six Overlooked Problems...) and one thing he mentioned that I found interesting is the thickness of the gasket between the carburetor halves.
Lynn states the the gasket in the kits is ~ ⅓ the thickness of the original gasket and that will causing idling problems because it affects the height of the idle jet. Also check the float level. I check my actual float level with the engine running. Checking level on my Marvel Schebler Last edited by Y-Blockhead; 11-28-2022 at 01:00 PM. |
11-28-2022, 11:42 AM | #5 |
Senior Member
Join Date: Jul 2010
Location: Pennsylvania
Posts: 1,100
|
Re: Model A Runs rich after Carb rebuild
Did you replace the original jets with the jets in the rebuild kit? Could be the new jets are a little oversized.
|
11-28-2022, 11:58 AM | #6 |
Senior Member
Join Date: Feb 2011
Posts: 2,113
|
Re: Model A Runs rich after Carb rebuild
Sponsored Links (Register now to hide all advertisements)
__________________
Tim Downtown, Ca |
11-28-2022, 12:11 PM | #7 | |
Senior Member
Join Date: May 2016
Location: Glide, Oregon
Posts: 1,339
|
Re: Model A Runs rich after Carb rebuild
Quote:
__________________
Ruth "Sometimes you really DO need to read the whole thread" |
|
11-28-2022, 12:29 PM | #8 |
Senior Member
Join Date: Sep 2022
Location: Canton, Michigan
Posts: 118
|
Re: Model A Runs rich after Carb rebuild
I used the new jets provided in the kit from Snyders. I still have the original jets if I need to put them back in
|
11-28-2022, 12:30 PM | #9 |
Senior Member
Join Date: Jan 2022
Posts: 723
|
Re: Model A Runs rich after Carb rebuild
Any of the above comments could be your problem, possibly more than one. In my limited experience virtually everybody sets the float level too high. A 90 year old gentleman in our club ran a Model A restoration shop for over 25 years and he showed me about it. If you set the float level so that it is level when you hold the top upside down you are too rich. I have found that most people who “rebuild” a Zenith really do nothing more than clean it (and usually not well enough) I am fascinated about the ideas of the gasket being too thin. What to do about it? Is anybody aware of how thick the gasket should be? Should we use 3 new gaskets?
|
11-28-2022, 12:51 PM | #10 |
Senior Member
Join Date: Jan 2022
Posts: 723
|
Re: Model A Runs rich after Carb rebuild
If I could find a Marvel at a reasonable cost I would love to try one.
|
11-28-2022, 12:53 PM | #11 | |
Senior Member
Join Date: Jul 2011
Location: Redondo Beach, CA
Posts: 5,849
|
Re: Model A Runs rich after Carb rebuild
Quote:
I use 1/32" ButaN/Cork and cut my own for my Marvels. Last edited by Y-Blockhead; 11-28-2022 at 12:59 PM. |
|
11-28-2022, 08:10 PM | #12 |
Senior Member
Join Date: May 2010
Location: Huntington, NY
Posts: 271
|
Re: Model A Runs rich after Carb rebuild
You don’t say so, but I assume this is a Zenith Carburetor. If so, the standard rebuild kits contain all four jets ............. AND A “REPLACEMENT BRASS VALVE SEAT” that installs in the Gas Adjusting Valve Chamber (commonly referred to as “GAV”) IN 28/29 CARBURETORS. This brass seat can be mistaken for the COMPENSATOR JET in the bottom of the gas bowl in the lower carburetor body. They look much the same, but the VALVE SEAT has a much larger hole in the center than the COMPENSATOR JET. If you installed the valve seat instead of the compensator jet, (or switched the two by mistake) the carb will run “extremely rich” and idle very poorly.
Good luck. Bob Bader |
11-29-2022, 12:11 AM | #13 |
Senior Member
Join Date: Jan 2022
Posts: 723
|
Re: Model A Runs rich after Carb rebuild
I spoke to Davis Renner this morning about the gasket thickness (BTW he’s still selling his jets). He said that .020-.030 would be correct. 3/64” = .050” so who knows? He did say that he didn’t think a gasket that was too thin would be much of a problem but a thicker than spec would be more likely to cause problems. I think more research is required....
|
11-29-2022, 12:19 PM | #14 |
Senior Member
Join Date: May 2010
Location: Portland OR
Posts: 6,342
|
Re: Model A Runs rich after Carb rebuild
If the jets are being flooded because the thickness of the gasket is suspect, then that can be taken care of by shimming the float valve to get the proper level in the bowl. Also making sure all old gaskets are removed before installing the jets.
When is it running rich? If at idle, have you adjusted the air/fuel valve? I start at about 1-1/2 turns open.
__________________
I know the voices aren't real but damn they have some good ideas! |
11-29-2022, 12:25 PM | #15 |
Senior Member
Join Date: May 2010
Location: Clinton,WA/Whidbey Island
Posts: 4,106
|
Re: Model A Runs rich after Carb rebuild
Jet length is important!!! and dished ends.
__________________
www.whidbeymodelaclub.com Last edited by Gary WA; 12-30-2023 at 02:36 PM. |
11-29-2022, 02:09 PM | #16 |
Senior Member
Join Date: Jun 2015
Location: Signal Mtn, TN (SE TN)
Posts: 2,372
|
Re: Model A Runs rich after Carb rebuild
My experience (albeit limited compared to many) with repop jets has been bad!
Cleaning old jets and flow testing is the only way to go. |
11-29-2022, 03:30 PM | #17 |
Senior Member
Join Date: May 2010
Location: Clinton,WA/Whidbey Island
Posts: 4,106
|
Re: Model A Runs rich after Carb rebuild
All jets purchased should be tested and checked for length-old ones too, for proper flow.
__________________
www.whidbeymodelaclub.com |
11-30-2022, 01:07 PM | #18 |
Senior Member
Join Date: Jun 2015
Location: Red Deer, Alberta
Posts: 5,046
|
Re: Model A Runs rich after Carb rebuild
FWIW, Jet sizes: The original Ford/Zenith carburetor jet number found stamped on the jet is the orifice size as expressed in 0.05mm increments. For example a jet marked number ‘18’ has an orifice diameter of ‘18’ X ‘.05’ = .09mm = .035”
__________________
If you don't hear a rumor by 10 AM, start one!. Got my education out behind the barn! |
12-03-2022, 03:11 PM | #19 | |
Senior Member
Join Date: Mar 2012
Location: Ohio
Posts: 1,975
|
Re: Model A Runs rich after Carb rebuild
Quote:
I have a B carb and intake now though. |
|
12-03-2022, 05:38 PM | #20 |
Senior Member
Join Date: Dec 2013
Location: Waxahachie, Texas
Posts: 949
|
Re: Model A Runs rich after Carb rebuild
I'll admit going in that I'm not an expert when it comes to setting up and tuning a Zenith, although I have "rebuilt" a few of them with fairly good results. It sure seems to me that they are a tad fussy to get set up correctly, Maybe my Marvel has spoiled me.
|
03-02-2024, 08:32 PM | #21 |
Junior Member
Join Date: Oct 2017
Location: auckland,New Zealand
Posts: 7
|
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: 5,849
|
Re: Model A Runs rich after Carb rebuild
Quote:
|
|
Sponsored Links (Register now to hide all advertisements) |
|
03-02-2024, 09:14 PM | #23 | |
Senior Member
Join Date: Jun 2014
Location: Land of Lincoln
Posts: 3,131
|
Re: Model A Runs rich after Carb rebuild
Quote:
__________________
Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done |
|
03-02-2024, 10:07 PM | #24 |
Senior Member
Join Date: Jan 2022
Posts: 723
|
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.
|
03-04-2024, 03:35 PM | #25 |
Junior Member
Join Date: Apr 2022
Posts: 18
|
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.
|
03-04-2024, 04:53 PM | #26 |
Senior Member
Join Date: May 2010
Location: brentwood, ca
Posts: 4,247
|
Re: Model A Runs rich after Carb rebuild
Sponsored Links (Register now to hide all advertisements)
|
03-05-2024, 07:52 PM | #27 |
Senior Member
Join Date: May 2010
Location: La Mesa Ca
Posts: 1,166
|
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: 1,106
|
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 |
|
|
Sponsored Links (Register now to hide all advertisements) |
|