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My 51 is running really nice now with new points and condenser. However, the high speed shudder continues as before. When the car is warm, under heavy/moderate acceleration, it sputters and almost dies unless I back off on the accelerator. Then it smooths out and runs just fine. The two suspects are the coil and the fuel pump. How do I test each of them, short of replacing them? Or any other suggestions?

I believe the only way to test the coil without having special equipment is to swap it. If there are any gas stations left that have tuneup oscilloscopes they might be willing to test the car for a small fee and be able to give a yes or no. The condenser could also be marginal and sometimes causes strange problems.

Didn't find any 51 specs but 52 fuel pump output is 4-5 psi and 1 pint in 45 seconds. I would expect very close numbers should also be for 51. They give a number of 10" mercury for the vacuum portion at 240 rpm so that is probably the speed for fuel pump portion too. I think that would mean the idle speed is around 480 or close to the recommended.

You could disconnect the pump from carb and rig something up with a gravity feed to run the car while you test. I had problems with a partially clogged ceramic filter that wouldn't let enough gas thru at higher RPMs so if you have one, or even the screen in the fuel pump bowl, another possibility.

I had a bad condenser (- although it was a NOS from Kanter) which only played up when hot and even then, more at high engine revs. Total brief loss of firing for a few seconds, which when it returned caused a massive after-fire as gas had built up in exhaust.

Suggest swap it first for around $10. Even if not the problem, you'll have a spare. I thought it was a coil problem and forked out $80 for a new one which didn't fix the problem. But at least I now have a new coil and a working spare coil, which is original one! BTW, I also tried another original 1951 coil and it too was ok, suggesting that these very old coils can be OK despite being 60-plus years old.

Though I wouldn't discount an ignition problem, I think fuel starvation is the more likely cause and thus I'd do the fuel pump check that HH56 suggested and I'd do it sooner rather than later. If in fact that's the cause the diaphragm has likely begun to rupture which means that you could be pumping raw gasoline into the crankcase, not only unsafe, but it can result in oil dilution and engine damage.

If that is the cause, of course an immediate oil change is in order before you run the engine again.

There is an issue that I found with my car. Check the fuel cap to make sure that it allows air into the fuel tank when running. I received my 51 with a fuel cap that turned out to be a radiator cap. I let in enough to air to run but not accelerate properly. But it was a nice fit. I am waiting for my new one from Tucsan Auto. They are supposed to be vented right?

They are supposed to be vented right?

Absolutely. Otherwise your pump would be trying to pull against a partial vacuum!

I will try the fuel pump test, and will rig up a bottle feed to keep the car running for 45 seconds and see how that works. I know it's not the condenser, as I had the exact symptoms with the old condenser I had on the car. I'll also check the gas cap - mine had a radiator cap on it as well when I got it.

I use an oscilloscope these days to look at waveforms.

For this case there isn't a lot of data.

I would do a warm compression test just to make sure the motor can pull the fuel.

Next, I would do a good old fashioned pump test using a vacuum/pressure gauge. As well, pump capacity into a bottle running with fuel line disconnected. You can use a T fitting with rubber hose and line ends. I love my homemade tools.

For ignition, why not get the car into misfire mode and keep it there as long as possible. Then kill the ignition, coast to a stop, and look at plugs. If the plugs are white/clean then it's a fuel problem. If they are sooty then it is ignition.

The gas cap thing is a good case. Take the thing off and road test the car. If there is an air leak in the lines the cap may be aggravating the situation.

You can test a coil on the road using a scope, but a an adjustable spark tester from NAPA may help with a low voltage problem. Another test is using a dwell meter. If the dwell is changing with RPM there is slop in the distributor drive.

Hope this helps.

hello:
I have a 1952 with the same symptoms. I have read all the posts thus far. I know my fuel filter is clean, the fuel pump is new. new points, condenser , etc. the coil is only a few years old.....
I will check my fuel cap again.
I have read other posts and I was wondering if I could have an issue with the vac. advance.????
thanks for the info.
tim