backfire under heavy acceleration

[dzolotarchuk]

I just rebuilt the carburetor on my 1966 T-bird. 390, autolite 4100. It runs much better at idle now and starts easier, but under heavy acceleration it backfires. It did not do this before the rebuild. On the road if you put the pedal to the floor, you get good initial acceleration for a second or two then it backfires. If you keep into the pedal it will accelerate again for a second or two and then another backfire.

I've tried increasing the primary float level, disconnecting the secondary throttle linkage, disconnecting the vacuum advance line from the carburetor to try to diagnose this, but none of these made any real difference.

The accelerator pump seems to be putting in a good squirt of fuel when I check it with the engine off.

Not sure what else to check or try from here. Any help or suggestions would be appreciated. Thanks.

 

[sseebart]

I know it's easy to blame the carb after a rebuild, but the symptoms sound more like a weak coil.

 

[dzolotarchuk]

Well, you were basically right. I had replaced the plug wires last weekend and thought it was running ok, but I must not have ever gotten hard into the throttle. I found that the coil wire was not seated properly into the distributor. The backfire is gone now. Sometimes it just takes someone looking outside the problem to make you look at the obvious. Thanks for your help.