I have a 73 roadster with a base 350 motor. I have been trying to do mechanical work myself with very little training by using the GM service manual for guidance. Last year I rebuilt the carb due to flooding problem. It seemed to be successful, but I also had a problem with engine performance..the car was not quick off the line and also surged and missed when it went into the secondaries.. I decided to do some further work which consisted of new plugs, points and wires. I bought a timing light and a dwell meter. The dwell is at 30 degrees and the timing is at 12 degrees BTDC. I think these are both in spec. I now have a problem with the car backfiring through the exhaust wen accelerating...When I check the plugs, they appear to be carbon fouled..but the most puzzling thing is that if I remove the number 1 plug wire while the car is running it has no effect...This is also the case with the number 3 wire...but if I remove others, the engine slows and runs more roughly...I have read everything I can on the net to try to find a solution and the only thing I can see is that perhaps I am getting crossfire in the plug wires??? When I replaced the wires I bought a high performance wire rather than original equipment wires...I was also wondering if it could be a weak coil??? Any help you can give me would be most appreciated.
Dan

 

It sounds like you have two plug wires crossed.

 

Or a bad air leak at the Intake manifold..... Double check your wires first then check for air leaks!!!

 

I agree,almost certainly sounds like an intake manifold leak at the 1,3 area and we all know the intake gaskets are known for this.Try spraying some carb cleaner in that area and note any change in the rpm,s.
Jules

 

Thanks for the responses...I will try the plugs first..then the intake. Pardon my lack of knowledge..but exactly where should I try spraying the carb cleaner??
Dan