Classic/Antique Car Repair: High speed miss 1951 Plymouth, older cars, transmission problems

Question
Hi Brad-

I had my 1951 Plymouth Cranbrook out this weekend (1st drive of the year) and out on the highway it wouldn't do over 45 mph and really slowed down going up a hill. Gas pedal was to the floor and seemed like the engine was missing. Going down hill it would sound better but when under load it would start to miss. Took it back home after about 15 minutes of driving- didn't want to be left stranded, shut it off to open the garage door, then it started real hard. No problem 2 years ago but last year I had clutch/transmission problems so I didn't drive it that much and only around town. Clutch/transmission problems fixed at a shop that works on older cars but I can't think of a connection between working on the clutch/transmission and a high speed miss other than the problem happened after it was fixed. Plugs/points/coil/condenser are about 7 years old but have less than 1500 miles on them. Every fall Sta-Bil is put in the gas and tank is topped off.

Ideas on what to check?

Thanks,
Jim

Answer
First do you have a fuel filter on the car? If so there could be some restriction in the filter like dirt build up. I would pull the plugs and get a look at them. With driving so few miles the plugs could be fowled a bit. A defect in the ignition coil  could also cause the same problem. Also check the exhaust system for restriction. It has not been unknown for critters to crawl in the tail pipe and build nests plugging the exhaust, and also check the air cleaner.