[CowtownCobra]

Car is running great, but recently it has developed a backfire on the left side (none from the right). Letting off big time leads to a big pop, while normal slow downs lead to mutiple smaller pops. It didn't use to do this. What do I check for, fouled plug, bad plug wire, or what. I'm clueless...

Have hydraulic lifters so I don't think a valve is sticking open.

Ideas?