Listen to Jerry and follow his advice. But if you want something quick and easy to do while you are sourcing the compression tester or leak down tester….can try pulling one plug wire at a time. Be careful….easy to get zapped.
Each wire you pull SHOULD make the engine run worse by roughly the same percentage. If you pull a wire and it produces no change at all…that cylinder either isn’t firing or has a bad misfire. Might help you narrow down and eliminate simple things like fouled plugs, bad spark wires, or valve issues (bad adjustment, bent pushrod, etc).
My well used and somewhat smoky 235 pulls down about 50 rpm on every cylinder once a wire is pulled. It’s probably half worn out, but it’s at least worn out evenly.
Did you ever check the vac advance?
Edit: On an engine that’s running badly already, it might be tough to interpret changes. But it’s a quick and easy test nonetheless. I’ve also seen a safer variation where you probe the spark plug boot with a grounded test light, rather than pulling the wire.
Last edited by JW51; 02/22/2022 5:50 PM.
