1929 Plymouth Model U Sedan

[elkhorne]

 

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I am new to the forum but have a 1929 Plymouth Model U sedan and have had a lot restored on the car. The carburetor that came on the car was a rebuilt Carter BB1 and ran for a while. It was discovered that the BB1 on the car was leaking fuel at the main metering screw and below the main body. It was also leaking air at the back of the gasket between the carb and intake manifold. We were going to rebuild our BB1 but got into it and check valve assembly had been damaged in a previous rebuild to the point I could not get it out. With that, we decided to replace the original BB1 with a NOS from Vintage Carburetors LTD. We received it and did final assembly after checking and double checking all gaskets and fittings. Friday night we re-installed the new BB1 with no real problems. We set the idle adjustment screw one turn out from the closed position. We set the main metering screw I turn out from the closed position. My wife started the car and it ran but at a very fast idle. Turning the idle adjustment screw in or out seemed to have no effect as with the main metering screw also had no affect. Due to the very fast idle we turned the car off. Saturday morning we went tried to start the car and it ran for about a minute then died. We noticed there was fuel leaking from the main metering screw and I tightened the main metering screw assembly on the washer to the lower carburetor casting. My wife tried to start it again and it did did not start! The next thing I noticed was that there was gas draining from the drain hole in the choke intake lower main body. This afternoon we again tried to start it but noticed there was very little fuel in the fuel filter I installed between the vacuum fuel cylinder and the BB1. The vacuum fuel cylinder had been checked out by our restoration mechanic and deemed good. He thought the petcock on the bottom of the cylinder was a sump drain but when I opened it, fuel stared to flow into the fuel filter. My wife started the car again with choke half out and the spark advance all the way out. The car started and I noticed fuel flowing from the vacuum fuel cylinder through the fuel filter. However, the car ran at a very fast idle and turning the idle adjustment screw in or out seemed to have no effect. Then I tried adjusting the main metering screw, albeit very hard to turn, and it did not seem to have any affect. In previous Carter BB1 discussions late last year, it was mentioned making “fine adjustments” but never went into what they were. Now I hope we have solved our fuel issue, we have to find out how to get the idle speed significantly reduced. I noticed when we shut it off tonight that it seemed hot from the running of about 5 minutes and that concerned me. My wife and I do not claim to be mechanics but we can follow directions and would appreciate any suggestions more experienced forum members could provide. Thanks in advance.

[keiser31]

1 hour ago, elkhorne said:

 

 

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I am new to the forum but have a 1929 Plymouth Model U sedan and have had a lot restored on the car. The carburetor that came on the car was a rebuilt Carter BB1 and ran for a while. It was discovered that the BB1 on the car was leaking fuel at the main metering screw and below the main body. It was also leaking air at the back of the gasket between the carb and intake manifold. We were going to rebuild our BB1 but got into it and check valve assembly had been damaged in a previous rebuild to the point I could not get it out. With that, we decided to replace the original BB1 with a NOS from Vintage Carburetors LTD. We received it and did final assembly after checking and double checking all gaskets and fittings. Friday night we re-installed the new BB1 with no real problems. We set the idle adjustment screw one turn out from the closed position. We set the main metering screw I turn out from the closed position. My wife started the car and it ran but at a very fast idle. Turning the idle adjustment screw in or out seemed to have no effect as with the main metering screw also had no affect. Due to the very fast idle we turned the car off. Saturday morning we went tried to start the car and it ran for about a minute then died. We noticed there was fuel leaking from the main metering screw and I tightened the main metering screw assembly on the washer to the lower carburetor casting. My wife tried to start it again and it did did not start! The next thing I noticed was that there was gas draining from the drain hole in the choke intake lower main body. This afternoon we again tried to start it but noticed there was very little fuel in the fuel filter I installed between the vacuum fuel cylinder and the BB1. The vacuum fuel cylinder had been checked out by our restoration mechanic and deemed good. He thought the petcock on the bottom of the cylinder was a sump drain but when I opened it, fuel stared to flow into the fuel filter. My wife started the car again with choke half out and the spark advance all the way out. The car started and I noticed fuel flowing from the vacuum fuel cylinder through the fuel filter. However, the car ran at a very fast idle and turning the idle adjustment screw in or out seemed to have no effect. Then I tried adjusting the main metering screw, albeit very hard to turn, and it did not seem to have any affect. In previous Carter BB1 discussions late last year, it was mentioned making “fine adjustments” but never went into what they were. Now I hope we have solved our fuel issue, we have to find out how to get the idle speed significantly reduced. I noticed when we shut it off tonight that it seemed hot from the running of about 5 minutes and that concerned me. My wife and I do not claim to be mechanics but we can follow directions and would appreciate any suggestions more experienced forum members could provide. Thanks in advance.

Have you seen these?

[Oldtech]

Fast idle - assuming no vacuum leaks, is usually caused by something (else) holding the butterfly open.  Possibilities are the linkage - may be different than the old one and not allow the carb to close to idle. Another possibility is that the butterfly is not seated correctly and mot allowing it to close properly. I would remove the carb and check the throttle butterfly operation. Make sure it closes tight, then is opened only by the idle speed screw, and not binding anywhere.

[elkhorne]

keiser31,

Thanks for the above info! Tomorrow we re going to move the pump link from the top screw hole to the lower hole to see how that affects the idle. Also we have our throttle link much further vertical than the example at the top photo 1. We will move ours back to about the 315 degree mark. Thanks for the help.

[elkhorne]

All, we found we had a gas flow problem until I tried the petcock on the bottom of the vacuum fuel cylinder. We had been told by a mechanic that it was a sump drain but in reality it is a fuel shutoff! once we had a good fuel supply flowing, we got the 1929 Plymouth U running for a few minutes but it was running at way too fast an idle and I shut it down. We had the spark advance about halfway out and the choke half way out. When my wife started to slowly to push the choke in and the idle seemed to speed up. I was uncomfortable with the high idle. We turned it off and it seemed to be hotter than before. Another issue is when the restoration mechanic returned the car to us, he had just found a small leak in the top area of the radiator and he put off having it repaired. It concerned me with the cooling system on the Plymouth not having a water pump. Anyway, I read more about the Cater BB1 updraft carb pre-1945. I removed the carb carefully to not disturb the new manifold gasket and found the throttle in the closed position is still open about 1/8+” and not fully closed. I am thinking the partially open throttle is why our idle is so high. While on the car, we cloaked the metering screw and opened it out 1/4 turn, 1 turn and 1 1/2 turns with no affect. Also we turned the idle adjustment screw the same from closed to open 1/2 turn, 1 1/2 turns and 2 turns with no affect. With this information can anyone offer in suggestions for us to get this car running smoothly again. Thanks in advance.

[F&J]

41 minutes ago, elkhorne said:

I removed the carb carefully to not disturb the new manifold gasket and found the throttle in the closed position is still open about 1/8+” and not fully closed. I am thinking the partially open throttle is why our idle is so high.

Yes, that butterfly or throttle plate should be able to be shut completely on most carbs brands, by loosening the "idle SPEED screw".

 

You don't want to to be totally closed, but your 1/8" is way too much.

 

Carb mixture adjustments won't have much effect if the throttle is too far open and engine running way to fast,  It has to be running at a slow idle to properly adjust idle mixture.

[elkhorne]

F&J,

Thanks for the suggestion. I will do that and we will see how it works. Your comments about the mixture screws makes sense if the idle is so high. Thanks again.

[Oldtech]

What is holding the butterfly open?  just a crack would be normal idle. If the shaft is binding you can loosen the 2 screws that hold the throttle plate and wiggle it around so that it closes properly. Then with it closed tighten the screws.

[elkhorne]

Old tech,

thanks for the idea. I just got through loosening the the screw for the piece connecting to the pump arm assembly and minimizing the throttle adjusting screw. Then it was still tight and I gave the throttle valve shaft a couple of smart links with my leather mallet from the left. The throttle valve seemed to be slightly rubbing on the left and it seemed to loosen it up to where it moves more freely now. The throttle valve now closes to within possibly 1/64” or less but much better than the 1/8” it was before. I also screwed the idle adjustment screw and the main metering screw/needle into the stop and backed each out 1/2 revolution. We will go back out shortly and reinstall. We are keeping our fingers crossed and saying our prayers that this solves our fast idle problem.

[elkhorne]

Oldtech and others on the forum that have spoke up. Oldtech’s comment about the excessive 1/8” opening on the throttle was spot on. Since my adjustments explained on the previous post, we got the Carter reinstalled on the Plymouth this morning. When my wife cranked it after our installation, the car started right up! She played with the choke cautiously and slowly pushed in in as the car warmed up. Then she pushed in the spark advance and it continued to run. I turned the main metering screw out 1/2 turn to make it out one full revolution.the engine seemed to like that last move and ran better than it has run in a month! We came back after early afternoon errands and started it again and again it ran very well. After a while she is going to back it out and drive it for the first time in 3 weeks when the old carburetor started leaking. Thanks gain to all who made constructive inputs.

[keiser31]

Thanks for the update. That is GREAT news!

[elkhorne]

We still have to play with the main metering needle and the idle adjustment screw. I have the main metering needle now turned out one complete revolution from the closed position. I have not yet increased the idle adjustment screw past the initial 1/2 turn out from the stop. My wife drove it this afternoon in the yard and she said it hesitated and died once when she shifted it into second gear. Tomorrow before she drives it, I am going to increase the main metering screw another 1/2 turn open and see what happens. I do not want to increase both because it it runs better or if it runs worse, you do not know which affected it. Until tomorrow, at least it is running! My next job is to get the leak repaired in the top area of the radiator. Thanks all for the help again.

[Oldtech]

Glad you got it. To set the main metering screw you should get the engine warm to sorta normal temperature then set it idling with the hand throttle to roughly 30 mph highway speed, then turn the screw to where it runs best. This will give you a good initial setting, which you can tweak from there if need be.  The idle screw is similar but may not be as easy. Run at slow idle and turn it in until it starts to slow down, then turn it out just to where it runs smooth.  The instructions should be in the documentation above. 

[elkhorne]

We still have to play with the main metering needle and the idle adjustment screw. I have the main metering needle now turned out one complete revolution from the closed position. I have not yet increased the idle adjustment screw past the initial 1/2 turn out from the stop. My wife drove it this afternoon in the yard and she said it hesitated and died once when she shifted it into second gear. Tomorrow before she drives it, I am going to increase the main metering screw another 1/2 turn open and see what happens. I do not want to increase both because it it runs better or if it runs worse, you do not know which affected it. Until tomorrow, at least it is running! My next job is to get the leak repaired in the top area of the radiator. Thank you for the guidance! Follow up: That was yesterday, today I turned the metering needle another 1/2 turn making a total now of 1 1/2 turns. My wife drove it today and it did good and sounded good to me. I think we are going to leave well enough alone for now. I really appreciate everyone’s help to get the car back running. I think I am going to make one of the drain pipes from the bottom of the choke bowl and back up to the vacuum port near the top of the carburetor so fuel doesn’t run down from the choke drain to the area over the exhaust pipe. To me it is a safety thing!

[carbking]

Typically, a "starting point" on calibrations for these carburetors (assuming the throttle will completely close, as it should) is 1 full turn on the idle mixture screw, and 2 1/2 turns on the high speed screw.

 

These settings will virtually always allow the engine to start, and warm until hot; final adjustments may be made once the engine is hot.

 

Jon