rallyace
I have a 51 Plymouth with a flat head six. It starts and idles fine. It accelerates fine. I have a problem with it stuttering at steady throttle.  Float is set to factory standard. Plugs are new and look just a hair on the lean side. Points are properly set, dwell is good. Could this be a coil or condenser issue? It has been a long time since I have played with tuning an engine so I am sure I have forgotten a lot of troubleshooting tips.

Mike
Friar
I would first like you to use some instruments to gather some more information. Perform a compression test on each cylinder, both dry and light oil inserted. Its always good to have that info handy to compare for future engine health. Next can you do a compression leak down on each cylinder? Again a good diagnostic procedure and the recorded data can be used in the future. Follow this with putting a timing light on the marks and see if there is any correlation to the stuttering. Another effective instrument is the vacuum gauge. Is the needle steady? Any indication of a leak somewhere? Let us know what you find.....
rallyace
Vacuum gauge stutters slightly. As this happens while driving I cannot really see what is going on with the timing.
Friar
I was not expecting you to look at timing while driving, but rather while stationary with low-moderate RPM. As you've reported the vacuum gauge stutters slightly, the compression test is now more important especially a leak down if you can rig up the air lines and gauge. A leak down test where compressed air is inserted into the cylinder while at TDC and shut off the air and watch the gauge. A good cylinder will lose air slowly.  I suspect this is related to a valve, perhaps one is leaking.
rallyace
Problem solved. Issue was a lot more complicated than I expected. It involved the battery, voltage regulator and the coil. First, I determined that the battery would show 6.5 volts at rest and when running but if the amperage draw would increase for any reason (directional signals, brake lights etc) the voltage would drop to 4.5 volts. If the car was running for 10 or more minutes the voltage would stay at 4.5 volts. This told me I had an intermittent cell in the battery. I changed the battery and the problem was still there but not as bad as before. I did not like what I saw with how the charging system was working so I then did a cleaning and adjustment of the voltage regulator and that indicated that the regulator was not operating properly. I replaced it and that solved more of the problem. Next I changed the coil from the new one to a known good spare. Bingo, problem solved.  She runs like a top. NAPA gladly swapped out the bad, new coil and now I have a good running car with a new battery, coil, and voltage regulator.  
Friar
This is a GREAT follow up to a thread and is a good example on why this Discussion Forum exists. I was not even thinking electrical when first posted. I assumed that the electrical system had already been checked and in good working order. I think the lesson here is systematically checking each item under all conditions.

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