nkaminar
Well-known member
This is a good site for the Zenith carburetor: https://modela.org/default.html
Problem with Rebuilt Carburetor
- Thread starter shew01
- Start date
This is a common occurrence. No, Not the idle issue put forth! Folks pay someone to rebuild a component, and the first time something goes wrong, they come to Fordbarn for answered to problems that developed in the component they just paid someone for their rebuilding knowledge of that component. Not a bad way to go. BUT ……….. as a component rebuilder myself, I’d really prefer if the customer called me first. To begin with, I’ve just had a close relationship with the component I just rebuilt. I know what I did in the process and can immediately give suggestions of how to troubleshoot ……… BEFORE I might suggest you send the component back to me. The advantage to me ………… I’d like to know if I missed something. The advantage to the customer??????? You don’t spend days replacing other components and scratching your head BEFORE you might need to send it back to me anyway.
I’m not trying to reprimand, negate anyone’s useful comments or knowledge. Just trying to supply some useful logic to a possible nerve wracking situation. You entrusted your rebuilder with your confidence and your money in the first place. Why not continue the process when a problem develops. Good luck with your venture.
I’m not trying to reprimand, negate anyone’s useful comments or knowledge. Just trying to supply some useful logic to a possible nerve wracking situation. You entrusted your rebuilder with your confidence and your money in the first place. Why not continue the process when a problem develops. Good luck with your venture.
Marshall V. Daut
Well-known member
The fact that the OP stated the carb worked fine for the first 250 miles tells me the fault doesn't lie in what the rebuilder did or didn't do. If the rebuild had been botched, problems would have surfaced right away, not after 250 miles.
Assuming then that the rebuild was fine (with one caveat to follow), something went wrong during the long drive. Several good suggestions have been made so far, including clogged jets and internal parts that worked loose. If the rebuilder truly did a complete rebuild, and not just the usual new parts installation routine, that should have included drilling out the passageway plugs and cleaning out the passageways. I know some experienced Model A owners here advise against doing this. But just because a paperclip can be shoved through a passageway, that doesn't mean the passageway is unclogged enough to flow the required amount of fuel. It only proves that a paperclip will go through. If the rebuilder soaked the carb halves in a carb cleaner, some loosened gunk may have remained clinging to the passageway walls and has now congealed, blocking one or more passageways. These carbs have suffered through almost 95 years of use and dozens of indifferent owners and incompetent "mechanics". To take it for granted that the internal passageways are clear after all this time and abuse is a bit too optimistic for the pessimist in me. Why go to all the trouble and expense of rebuilding a Zenith carb without ensuring the passageways are COMPLETELY clear so that the carb can deliver the correct amount of fuel as it was designed to do? If all the other suggestions made so far do not pan out and the carb still doesn't run right, I'd ask the rebuilder if he did drill out the plugs and clean the passageways. To each his own way of doing things and that's his prerogative. But I never rebuild a Zenith without drilling out the plugs and running a wound metal guitar string through the passageways when possible. Compressed air is always blown through every hole I can find, including the really hard to see little one in the throat where the throttle plate operates. (Did you even know there is a hole there???)
O.K. Assuming once again the carb itself is not at fault because of the rebuilder's mistakes, here's an odd thing I once experienced on a long drive from Arizona to Iowa in the 1990's. The engine ran fine with a rebuilt Zenith carb for the first 500 miles, but then symptoms cropped up like the OP describes. A visual inspection of the carb beside I-40 in the New Mexican desert revealed that the choke arm had come loose from the choke driver's groove, allowing the choke valve to float free in its bore. That alternately caused the carb to act as if it was being choked when the choke plate fluttered closed. I could barely keep the engine running. Then the plate would rotate to a different position and the engine would run better, but still not right because the plate never returned to the perfectly horizontal plane where it lives. It turned out that the nub on the reproduction choke arm was too short to stay inside the choke driver's groove and had slipped out while I was driving, which in turn freed the choke shaft and plate to flop around. I removed the original choke arm from a spare carb I was carrying and put it on the mounted Zenith. Its nub was noticeably longer and stayed in the choke driver's groove. That solved the problem. The carb wasn't choking itself to death any more. I wonder if that defective repo choke arm is still lying in the New Mexico desert where I threw it as far as I could?
Check that the choke arm is still seated in the driver where it's supposed to be and that the choke shaft and plate do not flop around. That will create the problems you are experiencing. An unlikely event, but it did happen to me (everything does!). Why not to you, too?
Marshall
Assuming then that the rebuild was fine (with one caveat to follow), something went wrong during the long drive. Several good suggestions have been made so far, including clogged jets and internal parts that worked loose. If the rebuilder truly did a complete rebuild, and not just the usual new parts installation routine, that should have included drilling out the passageway plugs and cleaning out the passageways. I know some experienced Model A owners here advise against doing this. But just because a paperclip can be shoved through a passageway, that doesn't mean the passageway is unclogged enough to flow the required amount of fuel. It only proves that a paperclip will go through. If the rebuilder soaked the carb halves in a carb cleaner, some loosened gunk may have remained clinging to the passageway walls and has now congealed, blocking one or more passageways. These carbs have suffered through almost 95 years of use and dozens of indifferent owners and incompetent "mechanics". To take it for granted that the internal passageways are clear after all this time and abuse is a bit too optimistic for the pessimist in me. Why go to all the trouble and expense of rebuilding a Zenith carb without ensuring the passageways are COMPLETELY clear so that the carb can deliver the correct amount of fuel as it was designed to do? If all the other suggestions made so far do not pan out and the carb still doesn't run right, I'd ask the rebuilder if he did drill out the plugs and clean the passageways. To each his own way of doing things and that's his prerogative. But I never rebuild a Zenith without drilling out the plugs and running a wound metal guitar string through the passageways when possible. Compressed air is always blown through every hole I can find, including the really hard to see little one in the throat where the throttle plate operates. (Did you even know there is a hole there???)
O.K. Assuming once again the carb itself is not at fault because of the rebuilder's mistakes, here's an odd thing I once experienced on a long drive from Arizona to Iowa in the 1990's. The engine ran fine with a rebuilt Zenith carb for the first 500 miles, but then symptoms cropped up like the OP describes. A visual inspection of the carb beside I-40 in the New Mexican desert revealed that the choke arm had come loose from the choke driver's groove, allowing the choke valve to float free in its bore. That alternately caused the carb to act as if it was being choked when the choke plate fluttered closed. I could barely keep the engine running. Then the plate would rotate to a different position and the engine would run better, but still not right because the plate never returned to the perfectly horizontal plane where it lives. It turned out that the nub on the reproduction choke arm was too short to stay inside the choke driver's groove and had slipped out while I was driving, which in turn freed the choke shaft and plate to flop around. I removed the original choke arm from a spare carb I was carrying and put it on the mounted Zenith. Its nub was noticeably longer and stayed in the choke driver's groove. That solved the problem. The carb wasn't choking itself to death any more. I wonder if that defective repo choke arm is still lying in the New Mexico desert where I threw it as far as I could?
Check that the choke arm is still seated in the driver where it's supposed to be and that the choke shaft and plate do not flop around. That will create the problems you are experiencing. An unlikely event, but it did happen to me (everything does!). Why not to you, too?
Marshall
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Obviously it is running rich.....Perhaps the float is the problem...look at this Barn recent Post: https://www.fordbarn.com/forum/showthread.php?t=341326
shew01
Well-known member
I’m just getting back to this. It’s been a long workweek.
The float seems a little low, maybe 3/4”, instead of the recommended 5/8”. Is this close enough? I’ve seen many warnings about not bending the float. How would I adjust it? I’ve read about shims, but I don’t know what they look like.
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The float seems a little low, maybe 3/4”, instead of the recommended 5/8”. Is this close enough? I’ve seen many warnings about not bending the float. How would I adjust it? I’ve read about shims, but I don’t know what they look like.
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shew01
Well-known member
Hmmm… Maybe this what I need.
https://www.brattons.com/ZENITH-FLOAT-VALVE-SHIM-KIT/productinfo/14341/
If the fuel level is low, do I need to add thickness? Or, use a thinner gasket on the float valve?
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https://www.brattons.com/ZENITH-FLOAT-VALVE-SHIM-KIT/productinfo/14341/
If the fuel level is low, do I need to add thickness? Or, use a thinner gasket on the float valve?
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If the float level was OK for the first 250 miles, why would you consider that to be the problem now?
Please don’t take this the wrong way. Your original post suggested you didn’t feel you could rebuild the carburetor yourself. You chose to select a rebuilder, feel some confidence in doing so, have said rebuilder do their thing, and spend good money to do so. Now, you’re “drawing at straws” trying to fix something you assume is wrong with a carburetor you didn’t trust yourself to rebuild but are now willing to rip into it with no more knowledge than you had before. Oh, and said rebuilt carb worked fine for 250 miles. Call the otherwise trusted rebuilder, explain the situation to them, ask for any consult they might have, and send it back if they suggest sending it back.
Please don’t take this the wrong way. Your original post suggested you didn’t feel you could rebuild the carburetor yourself. You chose to select a rebuilder, feel some confidence in doing so, have said rebuilder do their thing, and spend good money to do so. Now, you’re “drawing at straws” trying to fix something you assume is wrong with a carburetor you didn’t trust yourself to rebuild but are now willing to rip into it with no more knowledge than you had before. Oh, and said rebuilt carb worked fine for 250 miles. Call the otherwise trusted rebuilder, explain the situation to them, ask for any consult they might have, and send it back if they suggest sending it back.
shew01
Well-known member
Bob,
Please don’t take this the wrong way…. I’m not trying start an argument with you, but I don’t understand why you are giving me grief on this. I thought your response was harsh, and I have no idea why you are so annoyed. I’m legitimately trying to learn. Otherwise, I would not have posted.
Actually, I don’t consider the float to be the original problem. (I don’t recall saying that I did. Maybe I missed something in my post.) At the urging of folks in this post, I disassembled the carburetor (although I am definitely a newbie with carburetors, which I already made clear earlier) and cleaned out all the orifices that I could find with aerosol carburetor cleaner.
Yesterday, I finally had a little time to work on this again (I still work a full time job), and I put the reassembled carburetor on the car. While I had everything disconnected, I thought it was a good time to check the gas level. Being a newbie, I’ve never checked a float level before, and I really didn’t know where to start; so, based on web searches, Les Andrews, etc., I made a guess, and it looks a little low.
Since the car ran well for 250 miles, I don’t think the rebuilder is the problem either.
While waiting for responses about float level, I took the car for a test run, but I have not had a chance to post about that yet. So, here goes. The rebuilt carburetor does run better, but not quite as well as when it was rebuilt by the rebuilder. It idles (sometimes) around 450 RPM. It can climb a hill now.
Since I took the carburetor apart to clean it, I doubt I have any recourse with the rebuilder now.
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rich40701
Senior Member
Have you taken the float out of the carburetor and shook it to see if maybe it is leaking and has fuel in it? I have had cars suddenly start running really rich and found the float to be full of gas. Also I lesson I learned on these carburetors you can't adjust the idle jet unless your rpm is really low like 400 I am thinking. At 1000 rpm the idle jet has been bypassed and no amount of adjustment will make a difference in idle. If you are leaking with fuel valve turned on your float is too high or possibly a gasket has been left off of a jet.
shew01
Well-known member
Yes, I removed the float so that I could remove the float valve for cleaning. I couldn’t hear any fluid in the float when I shook it.
The weird thing was that the car would idle around 500 when in the garage (before my cleaning), but would not idle lower than 1000 when on the road in our neighborhood. Maybe getting warmer on the road influenced that?
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shew01
Well-known member
When you posted this, I wasn’t sure what you meant. However, when I cleaned the carburetor, I couldn’t see through the end of what I thought was the idle jet like I can see through the end of a straw. I sprayed aerosol carburetor cleaner through it. The car is performing better now. Thanks for the post.
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shew01
Well-known member
They seemed tight when I removed them and reinstalled them.
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shew01
Well-known member
In that picture, maybe I was using the caliper incorrectly. I took another picture of the caliper when set to the same position. I was attempting to set it at 5/8”. What do you think? See the 0 on the inch scale in this picture? Am I reading it wrong?
Today, it’s a moot point. I don’t have any shims to change anything.
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shew01
Well-known member
With full retard, the engine now (barely) idles at 500 RPM. I have the idle air mixture screw set at 1.5 turns open.
The engine about 168 degrees in the garage with a 160 degree thermostat.
When advanced, it doesn’t want to idle lower than 700, which is an improvement over the initial 1000 RPM.
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The engine about 168 degrees in the garage with a 160 degree thermostat.
When advanced, it doesn’t want to idle lower than 700, which is an improvement over the initial 1000 RPM.
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Brentwood Bob
Well-known member
The gav adjustment, the knob on the end of the choke rod, affects the idle. As the motor warms up, the adjustment changes. I think the owners manual goes thru the starting procedure. Dirty fuel is a common enough problem for me. I have had several returns (rebuilts) with this issue.
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