My Malibu, 305 on propane, is really starting to frustrate me... It started by backfiring out of the mixer (carb) under heavy load. threw a cap rotor and coil at it and it was fixed for about 2 weeks before doing it again. So i then changed the fuel filter, and plugs and wires, which i could tell really needed to be done. Cylinders 7 and 8 had blown their electrodes out of the plugs. Again this fixed it for about 2 weeks. Now it has started to sputter, worse at low rpms than high rpms. Once in a while it will still backfire under heavy load. I started thinking camshaft or bad valve, until yesterday evening when it ran just fine. This morning it is sputtering again, not quite as bad as before, but obviously the problem still exists. I have swapped distributors with no luck. The only clue i have is the #2 spark plug is dark, as if it's not firing. all the other plugs i replaced, the porcelin is still white with slight burn marks. I'm thinking intermittent spark, as i've changed that plug and wire, and got zapped once when i was checking for spark. But even so, what would cause that?
