Engine idles & runs perfectly when cold, responsive to the gas pedal, plenty of power, but as it warms up after 15 minutes of driving it starts to sputter and misfire. First symptom, pressing on the gas pedal to accelerate from 25 mph, very noticeable hesitation. A few minutes after that, balks when attempting to go over 40 mph. 10-15 minutes after that the performance gets much worse, hard to keep running, and stalls at idle, even in neutral.
Engine was due for new points anyway, so I did that first. No change, engine still performs perfectly when cold, sputters and eventually stalls when fully warm.
Considered the possibility of a clogged-carb, thinking it was going way too lean as the engine warmed up and the auto-choke plate went to full open. So starting w/a cold engine I removed the air cleaner and watched the choke plate as the engine warmed up. No difference comparing a cold engine, choke plate nearly closed to warm engine, choke plate fully open. Idled and responded to gas pedal normally in both cases. After another 10 minutes of idling, engine warmed further, choke plate still fully open, starts to sputter and shake at idle, poor response to gas pedal. Exhaust pulse feels like engine is missing.
Immediately after it stalled in neutral I popped the top off the carb. Float horizontal,
fuel bowl level is correct. Measured fuel pump delivery rate, in spec.
I’m guessing the results above indicate a problem due to something in the engine compartment getting hot. I’m thinking coil or condenser. Any other ideas?