Hi, Ive been having a good deal of trouble with my Zenith Carburetor. The 1930 A Truck will stall when I come to a stop. I know this story is very familiar but Im wondering if some one knows of guaranteed rebuild kit or maybe a qualified rebuilder? I have soaked this carburetor body in kerosene, floor stripper solution and the crap in a can from Orieleys. Ive spent much time with skinny wire poking through the passageways until my back was killing me. Ive played with different shim washers but I also have the problem of gas leaking from the overflow hole. And yup Ive cleaned and installed a few different needle valves. Couple years ago I sold a five window coup that ran fantastically, I lament not keeping the carburetor. God bless, thanks.
Zenith rebuild kit
- Thread starter Gino
- Start date
Marshall V. Daut
Well-known member
Here's the first of 10,000 pieces of advice on carburetors to follow.
Firstly, contrary to logic, LOWER the float level to reduce the tendency for the engine to die when coming to a stop. Set the level height as most sources state and then lower the level slightly, meaning with the upper carb half upside down, shim the needle and seat assembly so that the float sticks up a little higher. That in effect lowers the float and level of the gasoline in the bowl when the upper half is inverted and installed.
If you do order a so-called "rebuild" kit, toss the jets that come with it. They are usually grossly out of spec and are thrown into the kit by the manufacturer because their thread size fits in a Zenith carburetor, not because they are correct. These jets come from all sorts of applications, such as tractors and smaller CID engines. Their flow rates do not meet a Model A's needs. Often even the jet tips are shaped incorrectly and create fuel seepage and leakage. You already have a new needle and seat, so if you must order a rebuild kit for a Zenith - after first lowering the float level - buy only a gasket kit and order a flow-tested set of jets from Renner's Corner, although the kit comes with jet gaskets. Kind of pricey for the full set at around $60, but they are worth the money. They will supply the correct amount of fuel via their adjusted flow rate required by a Model A and their tips are of the correct contours to prevent seepage.
Marshall
Firstly, contrary to logic, LOWER the float level to reduce the tendency for the engine to die when coming to a stop. Set the level height as most sources state and then lower the level slightly, meaning with the upper carb half upside down, shim the needle and seat assembly so that the float sticks up a little higher. That in effect lowers the float and level of the gasoline in the bowl when the upper half is inverted and installed.
If you do order a so-called "rebuild" kit, toss the jets that come with it. They are usually grossly out of spec and are thrown into the kit by the manufacturer because their thread size fits in a Zenith carburetor, not because they are correct. These jets come from all sorts of applications, such as tractors and smaller CID engines. Their flow rates do not meet a Model A's needs. Often even the jet tips are shaped incorrectly and create fuel seepage and leakage. You already have a new needle and seat, so if you must order a rebuild kit for a Zenith - after first lowering the float level - buy only a gasket kit and order a flow-tested set of jets from Renner's Corner, although the kit comes with jet gaskets. Kind of pricey for the full set at around $60, but they are worth the money. They will supply the correct amount of fuel via their adjusted flow rate required by a Model A and their tips are of the correct contours to prevent seepage.
Marshall
Gary WA
Well-known member
OK all clean-make sure you have only (one) washer on each jet an they are tight! NO washer on Idle Jet! Set the float bowl like it was done 80 years ago-as per instructions.The float is adjusted to be parallel to the machined surface of the inverted upper body. Jets need to be flow tested and of proper length and end shape!!! Concave! Also ensure your float hinge pin holder is not loose-solder if it is.
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Gary WA
Well-known member
Site Index (Model-A.org) thanks to site owner good info.
Gino, X 2 on Marshal's, Gary's and JB's advice. The hole on the back side / engine side of the carb is not for overflow, it's for atmospheric air pressure to reach the tops of the idle jet, the secondary well, and the float bowl.
It sounds like your float valve isn't seating correctly. When you order your Renner's jets, he also sells a nice fuel level gauge. Using the gauge will tell you where the level is as the carb sets when on the car and whether or not the needle valve is leaking over time.
Needle valves leak for multiple reasons, but one of the common ones is that a dimple is worn into the float arm where it rides against the needle. This dimple causes a sideways push that lets the needle fail to seat fully.
It sounds like your float valve isn't seating correctly. When you order your Renner's jets, he also sells a nice fuel level gauge. Using the gauge will tell you where the level is as the carb sets when on the car and whether or not the needle valve is leaking over time.
Needle valves leak for multiple reasons, but one of the common ones is that a dimple is worn into the float arm where it rides against the needle. This dimple causes a sideways push that lets the needle fail to seat fully.
Marshall V. Daut
Well-known member
Marshall, you are slipping ol' buddy.
FIRST THING you used to preach was to set the Idle Speed as per the Owner's Manual, p24.
Yup! I guess maybe I am slipping a little. Who among us ISN'T?
Or maybe I take too much for granted and assumed the poster had moved up the idle. If the idle were too low, however, I should think the engine would want to die even while idling and before coming to a stop, possibly even between shifts. I think between what the poster has already done and if he follows the suggestions made in this thread, his stalling when coming to a stop problem will be solved. If the engine runs fine otherwise, the source of the stalling is bound to be one of the items mentioned so far. I still vote for the float level being too high. Lots of stalling Model A's on this discussion forum have been fixed over the years by lowering the level.
Marshall, on a slippery slope
FIRST THING you used to preach was to set the Idle Speed as per the Owner's Manual, p24.
Yup! I guess maybe I am slipping a little. Who among us ISN'T?
Or maybe I take too much for granted and assumed the poster had moved up the idle. If the idle were too low, however, I should think the engine would want to die even while idling and before coming to a stop, possibly even between shifts. I think between what the poster has already done and if he follows the suggestions made in this thread, his stalling when coming to a stop problem will be solved. If the engine runs fine otherwise, the source of the stalling is bound to be one of the items mentioned so far. I still vote for the float level being too high. Lots of stalling Model A's on this discussion forum have been fixed over the years by lowering the level.Marshall, on a slippery slope
Here's a helpful hint that might not be thought of. I've rebuilt carbs for customers and road tested and leak tested them for 48 hours with the gas valve open before sending the carb to the customer. Naturally, before packaging, I drain every bit of gas out of the carb and wrap it in packaging material. I've had some customers then call me saying that as soon as they turned on the gas, it poured out of the throat or the inboard air vent hole. I suggest that, if this happens to you, instead of panicking, shut the gas valve off and start the car normally. As soon as it starts, turn the gas back on and let the engine run for a few minutes. THEN, shut the engine off. You may be surprised to find that the engine needed to run to properly seat the float valve ......... even if you tested it by blowing into it before you installed the carb on the car. Good luck.
Gene F
Well-known member
I tend to agree with Marshall. The jets are not always correct. A little piece of wire, and removing them to spray some carb cleaner down them usually does the trick. If possible, taking the time to set the float with that little clear tube gadget to get the fuel level correct is a one-and-done type of thing. If you float is bad you will know it right away because when you shake it you will feel the trapped fuel sloshing in it. Otherwise just a little labor, and a couple of gaskets will fix you right up.
Very true I found the same thing. Maybe it has to do with what happens with carb laying on its side during shipping?
Even if you just put the carb in a box in the car trunk for a while it sometimes leaks after installing but this trick works.
Also when starting with a hot engine some carbs do not require choking while some carbs do need choking.
Also many carbs start easier hot or cold when the throttle is opened 2-3 clicks.
Ed in Maine
Well-known member
These carburetor topics are one of my favorites and I liked Benson's summation in that no two carburetors act the same. There are so many things in the design that can result in less than perfect operation. I wish I could say that I know why a particular carburetor stalls on slow downs. I have actually created stalling Model As after rebuilding a carburetor! But I think we all can agree on the following:
1. As the Model A comes to a stop, the engine is running slower and rougher than during normal idle conditions. In most cases, if you are quick enough with the throttle lever, you can stop the impending stall before it happens.
2. My car is always close to a stall when I start the turn into my driveway.
3. If your car is not idling smoothly, this will only make things worse and most likely will force you to increase your idle speed adjustment.
4. I maintain that the engine is getting an insufficient amount of gas.
After studying how the carburetor works, I think the design is marginal, and when the moon and the stars are aligned, it seems to work pretty well. Here is what I think is happening. When you approach a stop sign, the first thing you do is take your foot off the gas pedal. At this instant, the flow of gas into the engine from the Main Jet is cut off. Flow from the Cap Jet has been off for some time because the Cap Jet has nearly emptied the Secondary Well. There may be some gas coming through the GAV and Cap Jet but this is stopped when the throttle plate goes closed. At this same instant the only source of gas for the engine is through the Idle Jet. But, most likely there is very little gas available in the Secondary Well. I believe at this point it is a race between filling the Secondary Well and establishing gas flow to the Idle Jet and a stalled engine. There is not a lot of gas in the Model A bowl. The volume of inside the bowl is largely taken up with the float. This distance between the float and the Compensator Jet is about 1/8 in. or less. Any gas movement in the bowl will only delay filling of the Secondary Well by the Compensator Jet. I have noticed that with the car sitting at an idle, speed up the engine and release the throttle does not make the car stumble. So the sudden decrease of engine speed is not the problem. De-acceleration is the problem.
So, where to go from here?? ED
1. As the Model A comes to a stop, the engine is running slower and rougher than during normal idle conditions. In most cases, if you are quick enough with the throttle lever, you can stop the impending stall before it happens.
2. My car is always close to a stall when I start the turn into my driveway.
3. If your car is not idling smoothly, this will only make things worse and most likely will force you to increase your idle speed adjustment.
4. I maintain that the engine is getting an insufficient amount of gas.
After studying how the carburetor works, I think the design is marginal, and when the moon and the stars are aligned, it seems to work pretty well. Here is what I think is happening. When you approach a stop sign, the first thing you do is take your foot off the gas pedal. At this instant, the flow of gas into the engine from the Main Jet is cut off. Flow from the Cap Jet has been off for some time because the Cap Jet has nearly emptied the Secondary Well. There may be some gas coming through the GAV and Cap Jet but this is stopped when the throttle plate goes closed. At this same instant the only source of gas for the engine is through the Idle Jet. But, most likely there is very little gas available in the Secondary Well. I believe at this point it is a race between filling the Secondary Well and establishing gas flow to the Idle Jet and a stalled engine. There is not a lot of gas in the Model A bowl. The volume of inside the bowl is largely taken up with the float. This distance between the float and the Compensator Jet is about 1/8 in. or less. Any gas movement in the bowl will only delay filling of the Secondary Well by the Compensator Jet. I have noticed that with the car sitting at an idle, speed up the engine and release the throttle does not make the car stumble. So the sudden decrease of engine speed is not the problem. De-acceleration is the problem.
So, where to go from here?? ED
Marshall V. Daut
Well-known member
It is not necessary to buy a "new" Zenith, nor especially bullet-proof. I have friends who have bought "new" Zeniths and their quality and performance are all over the map. I have had to go through three of them and correct problems. Others say they have had no problems with theirs. Too risky in my opinion and not necessary because there are so many original Zeniths out there to be had. A number of guys on this website rebuild them for less than the vendors charge for a new one, or you could buy a rebuilt one from Bert's Model A Center in Colorado. The quality of Steve's rebuilds is legendary. No risk, no problems. Quality.
But try to fix your carburetor first, not only to save a ton of money, but also for the satisfaction that you personally made a successful repair. You will also have learned a good deal more about repairing your Model A. That's a confidence booster for sure!
Marshall
But try to fix your carburetor first, not only to save a ton of money, but also for the satisfaction that you personally made a successful repair. You will also have learned a good deal more about repairing your Model A. That's a confidence booster for sure!
Marshall