Intermitent backfiring

[Rick Parker]

Intermitant missing is a "*itch" to track down. Knowing how the "Miss" feels is KEY. I like to desribe an electrical miss as a "Sharp" cylinder misfire heard in the exhaust, where a fuel related one is where the engine more or less noses over temporarily and then recovers; it "Sounds" different than electrical miss and it feels different too. I may be over simplifying this but if you have actually chased both and resolved them, you will know how the engine reacts to each.
Look at your wires near where they attach to the plugs, burned boots on the plugs or compromised wires near the headers, potential crossfiring (if electrical??) Be sure the center contact on the distributor cap is touching the spring contact on the rotor. Many of these parts are mixed by the manufacturers and not originally matched with each other. For example the Chevy style rotor adapted by MSD and their "Small Diameter Cap" and other applications, used in various applications. Hence the mismatch problem many of us unknowingly encounter. Also the more resistance created throughout the secondary system with resistor plugs, High Voltage Coils and resistance wires all create more heat being put into the carbon button of the distributor cap, thus affecting its life an that of the cap too.
I once was chasing an intermittant electrical miss and while actually adjusting and tuning found the plastic under the spring blade on the rotor eroded with a hole being burned, allowing the spark to jump grounding itself through to the distributor shaft.