What do higher than normal compression readings suggest?
Quick recap: Late 235. Starts easy. Runs ok at fast idle part choked. Try to slow the idle or push the choke in and it will stumble and die with a backfire through the carb. Also have a leaky Rochester B, FWIW.
Got some vac readings yesterday. Steady 15ish inches when running ok fast idle/ part choke. Slow the idle or push in the choke readings get much more erratic and much lower.
My next move was going to be advancing the timing a bit with the vac gauge hooked up. As well as making sure the float is adjusted and needle is seating.
But I got to wondering if maybe had a more significant issue with the bottom end, so I did a cold compression test tonight. I know cold isn't ideal but had been old by folks here that it's still work doing. Throttle blocked open. All plugs pulled.
Compression, I have. Maybe too much?
First round through I got readings from 130-150. A few spikes up higher that I ignored and reran. Did a second run through where I recorded the high spikes:
CYL - PSI
1 - 140
2 - 140
3 - 160? Redo 140
4 - 150? Redo 145
5 - 170? Redo 160
6 - 150? Redo 150
For what it's worth, #5 had a 140 on my first run.
What are these telling us? Exhaust valves not opening sometimes? Exhaust obstruction close to the manifold? Does this piece of the puzzle explain any of the symptoms while running?
Last edited by JW51; 01/27/2015 5:49 AM.
