Repro carb still too rich!

MrTube

MrTube

Well-known member
I'm running a repro carb from Brattons. I checked the float level and found it to be a hair low so I set it per spec knowing it would only make things worse.

Its of course still running too rich. Idling too rich and I have the Idle air screw as far out as I can get it without it falling out. I never need to open the GAV at all even when shes cold.

I'm thinking about putting the jets from the original carb into the reproduction, is it even worth my time? Has anyone found the reproduction jets to be too large?


I do not currently have an air cleaner installed, this is wide open to fresh air.
 
Why don't you give Walter Bratton a phone call and explaing the problem you're having with one of his carbs. I am sure he will be of help to you.
 
I agree with Frank above. I have rebuilt a lot of these and the jet flow test is important as well as jet length and many other factors. The originals are always the best it seems and that goes for most things on the Model A.
 
I would rather not contact Walter as this carburetor is well over a year old. Walter has been EXTREMELY helpful whenever I have had an issue and I would hate to bother him with something I can fix.

Reason I have left this problem so long as I have been continuously learning about the A as well as correcting other problems. I did not want to assume the carburetor was at fault and I still kind of wonder if something else is going on. This is why I had asked if anyone else had found the reproduction carburetors to be jetted wrong.
 
Installed 2 or 3 of the reproduction Zenith's (from Walt) and the only problem was the jets were not tight. Corrected that and they ran fine.
 
Hi Mag,

Wow, I could definitely see that causing this problem. I'll have a look ASAP.

thanks!
 
MrTube,
You said, "Idle air screw as far out as I can get it", if you mean " idle mixture
screw ", it's not an air bleed. Screw it in, to lean the mixture at idle.

Dudley
 
d.j. moordigian said:
MrTube,
You said, "Idle air screw as far out as I can get it", if you mean " idle mixture
screw ", it's not an air bleed. Screw it in, to lean the mixture at idle.

Dudley
Click to expand...


d.j. with all due respect I think you are mistaken. On the Zenith carburetor it is an air bleed screw. Full in is full rich.
 
MrTube,

If we are talking about the needle, to the front of the butterfly( throttle ), the
hole that it controls exits above the butterfly when closed, and is in a vacuum,
sucking fuel. I hope we are talking about the same thing.

Dudley
 
Dudley, Please see the following link for the flow diagram of the Zenith carburetor.

http://www.model-a.org/flow_diagram.pdf

Note the "mixing chamber" is after the mixture screw. The mixture screw controls air flow.

I currently have the screw turned out as far as possible and its still too rich. GAV is closed tight.
 
Mr Tube,

I do not know if the repro carb uses a GAV brass seat or not. But if someone swapped the comp jet with the GAV seat it will run WAY too rich as GAV seat is 3-4 times larger opening. Threads are same on original Zentih so it is easy to swap them.

Even if repro does not use GAV seat someone may have done the swap (i.e. used worng part) when the carb was assembled!

This shows GAV seat:
http://www.model-a.org/gav_seat.html

This page tells the size of Comp jet so you can check it out.
http://www.model-a.org/compensator_jet.html
 
Tore the carb apart today and compared everything to the original. I also switched the compensator jet with the original. No change.

The engine runs best after you shut the fuel off and let the bowl empty. Is there any chance the GAV is not seating properly? It feels good mechanically but I did not take it apart.
 
fordgarage said:
You are getting very close to proving the contention that properly restored original parts are better than new reproduction parts.
They typically fit and work better, and usually lower cost than repro. :D
Click to expand...


Yea. I am getting that exact feeling. :(
I'm going to take the GAV apart tomorrow. Something tells me thats where the problem is.

Does anyone know if the repro carbs from Brattons have a removable Jet in the GAV?
 
If you have not flow tested the jets you do not know where you are with the carb. I built one from the articles available in the magazines it took only 2-3 hours to put it together. Only one of my jets was within spec. when I tested them. Its not worth not being able to test the jets. Bill G
 
Is there a better source for accurately sized jets? I have two different idle jets from two different suppliers...each very different size aperture!
 
Dave Renner at Renners Corners (734-428-8424) can sell you a complete set of flow tested jets....
 
I found one of the repro carbs that the GAV threads were bad so it would not seat. You are on the right track.
 
b67 mentioned Dave Renner as a source and he is correct, Dave has excellent product and is a good guy to deal with. He will offer advice willingly when you need it. His contact info is:
Dave Renner
Renner's Corner, LLC.
10320 EAST AUSTIN ROAD
Manchester, Michigan 48158
1-734-428-8424
10:00am TO 4:00pm MON - SAT
DAVID@RENNERSCORNER.COM

I completed flow tests on a group of random jets in my box in preparation for a Technical Clinic I was presenting to our Twin Cities Model A Club. I have attached it below. It confirms what many have been saying about the varying flow rates of jets and why it is important to flow test and adjust them for a properly set up carb.

If you want to see the Clinic write-up for tuning of the Zenith Carb, go to the services page of my website and Click on the link to: Performance tuning of Zenith carburetors

Good Day!
Dave in MN
www.durableperformance.net
 

Attachments

If you had the same problem with new carb and old. Maybe the choke knob is turning and the shaft isn't ?? Had that happen to a club member. Cure, a new shaft. have someone watch the rod on the carb while you turn the knob. Tony
 
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