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Old 10-08-2020, 08:12 AM   #5
Bob Bidonde
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Join Date: May 2010
Location: Long Island, NY
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Default Re: Compression Test

The 0.100" over bore raises your engine's displacement to 211 cubic inches. A 6:1 compression ratio should produce about 90+ psig, so the compression readings you have are reasonable.
However, the difference between 100 psig and 92 psig is 8% which is a bit too much. Moreover, the variation in pressures between cylinders before and after the new head are inconsistent. The old head had a 6% variation which is borderline, but the high and low differences are not at the same cylinders as with the new head.
Repeat the compression test. Make sure you have all of the spark plugs out, and the carburetor throttle is wide open.
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