Re: 1941 Runs rough when warm

Posted by Bob J On 2022/11/25 10:56:57

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.