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Re: 1941 Runs rough when warm
#11
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Marty or Marston
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Right after it stops running, with the air cleaner off look down the carburetor and turn the throttle valve. If it squirts gas, I would think it is very doubtful that your problem is the fuel pump since the carb had gas at that time. Be prepared that if it didn't squirt gas to pour a couple of tablespoons of gas down the carb and try starting. If it fires up and then stops (because the 2T of gas is gone), I would lean towards a fuel problem with the carb.

If it doesn't try to start, I would lean towards an electrical problem. Check and clean all connections in the spark plug circuit. Replace the 1) coil 2) condensor, 3) distributor cap & rotor, and 5) the wire from it to the distributor. Replace any frayed and damaged wires in the spark circuit.

Posted on: 2022/11/25 9:55
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Re: 1941 Runs rough when warm
#12
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Bob J
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Another way to check the fuel pump and rule it out is to pressure test its output. On my vacuum gauge there is a positive side to the needle to show fuel pump pressure. I doubt that with it starting right up it will be the pump, but this test would rule it out.

As you have completely replaced the electrical side it isn't that. The same vacuum gauge will also show if any valves are sticking. When the car is running it should have a fairly steady needle. It will flutter a bit but big swings show a leakage, bad valves or timing can be the cause.
Compression test will rule out rings and valves too, they are worse when cold so that is unlikely to be it.
Some sparkplugs fail when hot, they are easy to pull and check to make sure they are all a nice tan colour, black and oily shows a bad one.
As it is a sneaky one look for weird reasons, check that all wiring is nowhere near hot surfaces. Oh, another weird one, the vacuum gauge may just show a steady low, check that the exhaust system is not clogged with a mouse nest, anything in the exhaust will really mess up a motor. Good luck chasing the gremlin! If it was simple no one would ever get rid of their cars!
Bob J.

Posted on: 2022/11/25 10:56
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Re: 1941 Runs rough when warm
#13
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JeromeSolberg
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I had a problem like this with a Volvo Amazon.

The car had a very slight pinhole leak in the float. You could run it for 5 or ten minutes, even get it going down the freeway, and then it would start running bad and die. Then you could start it up again after 5 or 10 minutes, repeat.

Posted on: 2022/11/25 13:09
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Re: 1941 Runs rough when warm
#14
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29tons
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Jerome your on the right track I found the problem and your not going to believe it. My brother-in-law said it was the fuel pump i did not believe it was but I thought I would try a electric pump. So I figured I would unhook the gas line and run the engine out of gas so the mechanical pump would not be pumping gas all over the place. I started the engine with the gas line disconnected and as always it was shimmy and shakeing but for the last minute or 2 the engine had smooth out. I said to myself the float must be adjusted wrong. I took the top of the carb off and I was looking at the float and needle and seat and I found a piece of hair in the needle and seat. I removed that put the carburetor back together and its been running smooth for a 1/2 hour. I think I got it.Sneeky in deed. I wanted to say thanks everyone for the replys

Posted on: 2022/11/25 13:35
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Re: 1941 Runs rough when warm
#15
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BigKev
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Great to hear you've solved the mystery!

Posted on: 2022/11/25 14:39
-BigKev


1954 Packard Clipper Deluxe Touring Sedan -> Registry | Project Blog

1937 Packard 115-C Convertible Coupe -> Registry | Project Blog
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Re: 1941 Runs rough when warm
#16
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Bob J
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So being bald turns out to be a plus when rebuilding carbs, good to know!!
Bob J.

Posted on: 2022/11/25 15:07
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Re: 1941 Runs rough when warm
#17
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tsherry
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This is a wild longshot, but have the rubber fuel lines been replaced? Old lines rot from the inside out, and the inner part of the line can suck closed under prolonged suction, causing a stumble or stall on acceleration. Shutting off the engine and ceasing suction allows fuel to flow again, but is repeatable. I've had this happen on several of my '60's Fords and my '37 115c. Lines looked fine on the outside, but were soft inside and had separated from the nylon cord centered in the cross section of the line.

Posted on: 2022/11/25 15:44
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