Hi, I’ve looked through a good amount of info here on the Ford Barn, also have looked at a website for Zenith carb issues. My question is if I have replaced all the innards with a kit from Snyder’s and have used carb cleaner, it seems more than likely that I would not have any debris or dirt to cause the engine to stall when coming to a stop. I purchased this carb from Snyder’s 8 years ago and have replaced parts many times but I still have to run it rich by way of keeping the gav open day 3/4 turn. I had so much carbon build up it caused the engine to knock. Thanks for any help, just when I start to think I know what I’m doing I get a quick reality check. Thanks again
Zenith carb
- Thread starter Gino
- Start date
Bob Bidonde
Well-known member
Typically, the cause of the engine running roughly or stalling when the car comes to a stop is the gasoline level in the float bowl is too low. As the car decelerates to a stop, gasoline surges forward in the float bowl. When too low, the gasoline surge uncovers the compensator jet which lets air into the idle jet well and cap jet and starves the engine of fuel.
(1) The engine needs to sit at a 3-degree angle in the frame to match the drive-line angle and level the carburetor with the frame. Fix this if necessary;
(2) Make sure there are no vacuum leaks before iterating the float level. A sneaky vacuum leak is through a vacuum windshield wiper motor if your car is so equipped. Other vacuum leak points are through a sloppy fitting carburetor throttle shaft and a poor fitting gasket;
(3) The 5/8" classic float setting is a starting point. The ideal float setting needs to be iterated as it will be slightly different from car-to-car. In this case, the float is too low, so raise it a tad and road test the car. Keep tweaking the float level until the car behaves properly when coming to a stop. Be sure the GAV is no more than a 1/4-turn open and the engine is at its operating temperature.
(1) The engine needs to sit at a 3-degree angle in the frame to match the drive-line angle and level the carburetor with the frame. Fix this if necessary;
(2) Make sure there are no vacuum leaks before iterating the float level. A sneaky vacuum leak is through a vacuum windshield wiper motor if your car is so equipped. Other vacuum leak points are through a sloppy fitting carburetor throttle shaft and a poor fitting gasket;
(3) The 5/8" classic float setting is a starting point. The ideal float setting needs to be iterated as it will be slightly different from car-to-car. In this case, the float is too low, so raise it a tad and road test the car. Keep tweaking the float level until the car behaves properly when coming to a stop. Be sure the GAV is no more than a 1/4-turn open and the engine is at its operating temperature.
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jayvee34
Senior Member
Tom Endy has a couple of articles on the Zenith. If you have not read them, look them up on line. I did and followed his instructions and did get my Zenith working much better, but it still runs lean as yours does. Tom mentions that the after market jets and some of the
new oem jets are either over or under drilled. I have ordered a set of drills from Drills Unlimited for the Model A Zenith jets. I should have them this coming Saturday or Monday at the latest. I will let you know the outcome if you PM me with your phone # or E-mail.
One of his articles give the correct jet opening sizes. They are: main & cap 63 MM, comp 65 MM, Idle 75 MM.
new oem jets are either over or under drilled. I have ordered a set of drills from Drills Unlimited for the Model A Zenith jets. I should have them this coming Saturday or Monday at the latest. I will let you know the outcome if you PM me with your phone # or E-mail.
One of his articles give the correct jet opening sizes. They are: main & cap 63 MM, comp 65 MM, Idle 75 MM.
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Gary WA
Well-known member
Float Level! Even replacing innards All jets with proper gaskets! Need to check all jets for length and proper diameter. no gasket on Idle jet only one on others.
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Thanks, I’m going to go through the carb again and check the 3 degree slant. For some reason I’m not able to pm you Jaycee. I’ve heard about drilling the jets out and I’m interested in knowing how it works please try to pm me. What do you guys think about rebuilt carbs from the dealers. Thanks
You said you purchased this carburetor from Snyder's but failed to mention if it was a new carb or a rebuilt original. Also, have you had this problem from the first time you installed the carb on the car or is the 3/4 turn open on the choke rod a new phenomenon? What was the status of your old carburetor? What made you replace it? Hard to diagnose a situation without all the info.
Patrick L.
Well-known member
When you cleaned the carburetor were the jets removed and the passages cleaned and blown out ?
It sounds as though that is your problem, to me anyway.
When you open it up and if you find debris in the bowl then you may want to consider an in-line filter. I know there are some that say they won't work, but, I use them with no issues.
It sounds as though that is your problem, to me anyway.
When you open it up and if you find debris in the bowl then you may want to consider an in-line filter. I know there are some that say they won't work, but, I use them with no issues.
dave hummell
Member
I had some problems with the zenith that was on my 31 and I cleaned and replaced the jets with the renners and it ran quite well for some time then it wanted to stall at stop signs and lights I turned the idle up a little bit not so you would have trouble shifting and it worked for that carb.
Good point. I had a NEW Zenith carburetor from Snyder's that ran extremely lean. Had to run with the GAV open 1½+ turns. Turns out the throttle shaft bore in the carb body was HUGE, allowing air in. I had to install an oversize throttle shaft to get it to run normally.
jayvee34
Senior Member
Mine had a similar problem, Had run 2 1/2 turns open.
The main jet bore was under sized, it is now drilled it to 63 MM and starts cold
with the throttle lever at 2 clicks, GAV at 1/8 open, until warmed up and runs
with GAV closed or just barely open. I have a set of jet drills coming so as to
check the comp and idle jet. It idles perfect though and the cap jet was already
at 63 MM.
jayvee34
Senior Member
I just PM you!
Ed in Maine
Well-known member
Gino, all of the comments above are very good. But, no one has mentioned that you should flow test the jets before you put them into the carb. I recommend you get "Zenith Model A Carburetor Restoration Guidelines" by Steve Pargeter sold by most of the parts suppliers. Using the correct drill sizes on the various jets is not good enough to set the correct flow. This is because the drill leaves the hole with small imperfections that change the flow capabilities of the jet. We are dealing with very small flow rates. Most often when I modify a jet by soldering them I use a piece of 24 ga. SST wire for the Idle Jet and 20 ga. for the other jets to keep the holes open. Solder does not stick to SST. I then remove the SST wire and use the jet drills as a round file to open the holes to get the flow correct. See the carb restoration manual on how to make the flow tester. After restoring many carbs, I feel the optimum flow numbers are as follows: Main Jet at 156 ml/min, Compensator at 141 ml/min, Cap Jet at 170 ml/min (not as critical as the others) and the Idle Jet at 46 ml/min. Occasionally, I have created a "staller" and I believe the culprit is the having the Compensator at the low end of its published range (138 or 139 ml/min. along with an Idle Jet at its low range of 44 ml/min. When you get to a stop sign, your foot comes off the accelerator and the throttle plate goes closed. All gas flow from the Cap Jet and the Main Jet is shutoff leaving only the Idle Jet to keep the engine running. Unfortunately, the Secondary Well is practically empty and this is the only source of gas for the Idle Jet. In this instant, it is a race between the engine stalling before the Secondary Well can refill from gas coming through the Compensator Jet. Some gas will also come through the GAV but it is a function of how far the GAV is open. Also, if the float level is too low, there will be no gas getting through Compensator Jet making things that much more worse.
In summation, if there are no vacuum leaks at the manifold, the throttle plate shaft fit is good, the carb is clean with flow tested jets, you can't help but have a Model A that runs as good as it came from the factory. Good luck, Ed
In summation, if there are no vacuum leaks at the manifold, the throttle plate shaft fit is good, the carb is clean with flow tested jets, you can't help but have a Model A that runs as good as it came from the factory. Good luck, Ed
Gary WA
Well-known member
#4 post did length and flow test
Wow! Where do I start. Bob thank you for taking the time to forward me the carb diagrams.
I purchased this rebuilt carb from Snyders 10 years ago and have replaced the guts maybe three times. I have to tell you I have a very mechanical mind I build and work with tools every day. Im an ok mechanic but in no way a machinist. For me, I see the follies of running a drill bit into a precision component. Im thinking its very likely Id be ordering a new kit in short order. If I could sell some of my wifes shoes Id just buy a few new carbs. How can tell if a carb is running lean or rich? How do you know the engine temp? I do not use a gauge. I believe I did an adequate job cleaning the carb, my hands are still pretty cold from spray carb cleaner. God bless and thanks very much.
I purchased this rebuilt carb from Snyders 10 years ago and have replaced the guts maybe three times. I have to tell you I have a very mechanical mind I build and work with tools every day. Im an ok mechanic but in no way a machinist. For me, I see the follies of running a drill bit into a precision component. Im thinking its very likely Id be ordering a new kit in short order. If I could sell some of my wifes shoes Id just buy a few new carbs. How can tell if a carb is running lean or rich? How do you know the engine temp? I do not use a gauge. I believe I did an adequate job cleaning the carb, my hands are still pretty cold from spray carb cleaner. God bless and thanks very much.
shew01
Well-known member
This works well for me. You can use it to take the temperature of the radiator (top, middle, bottom), water neck that goes to the radiator, engine head (front, middle, back), sides of the engine, oil pan, etc. You can use it to compare the temperature of each brake drum to see if one is dragging or not engaging as the other drums. It’s a handy tool.
Etekcity Lasergrip 800 Digital Infrared Thermometer Laser Temperature Gun Non-contact -58℉ - 1382℉ (-50℃ to 750℃), Yellow/ https://www.amazon.com/dp/B00DMI62HM/?tag=atomicindus08-20
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katy
Well-known member
Methinks that there's some confusion going on here,
#63 drill bit is .037" diameter
63 MM = 2.48"
jayvee34
Senior Member
#63 drill size = .037 inch.
Oh Oh, I goofed on the Millimeter, sorry, don't know where I got that, guess I need to bone
up on my conversion tables.