The van was running fine than the engine started back firing through the carburetor. Low compression across the line, + or - 5# (95# average) Intermitent missfire - replaced the cap, rotor, wires and plugs and missfire is still present. The coil is to be replaced next. The most pressing problem is the backfire through the carburetor. The backfire is not present at idle but during acceleration it is constant. Does anyone have some help for me?

1983 G 10, campervan, 305 cu. in. V8, Rochchester 4 barrel quadrajet carb, automatic

 

Timing issue? Could the dizzy have moved?
Sticking valves staying open letting compression pressure into intake? Or maybe a broken valve spring.
Pull your rocker arm covers and have a look.

 

Sounds like a bad exhaust lobe on the cam that vintage was pretty prown to that