Follow up to post of 9 / 5

'91 Crusader power loss issue posted first on 9 / 5. Had the marinas gas mechanic there today. Found timing way off on port side, like 18 degrees ! Makes no sense unless it was set wrong due to counter rotation. Or maybe something moved ? Anyway, runs much better, but still tops out at 3700 with both engines still even. Did a complete compression check, not as good as I would like, but both engines are consistent.
Flushed both engines with reccomended biodegradable acid and that appears to have helped a lot with the hot running issue.
Going to have both carbs rebuilt, never done in twenty years, guess it's time. May also drop an inch or two of prop pitch to see if that will bring the r's up some.
Thank you all very much for your help and interest !!

Surely your prop pitch reduction in increase RPM but if you have had the boat running at higher WOT you may just be covering up the real issue. Props are not a cheap soultion if it is not the real problem. Carb rebuild is certainly a great idea as after 20 years there is wear. What were the compression figures when tested?

AND I am interested in the acid flush....what is that product?

As to compression, all cylinders were 105 to 120, none real low or too high, plugs looked good. The acid engine bath is called " boat magic "

I sent for some a few moments ago. I was always instructed that a cylinder pressure of 100 or less is considered a dead cylinder, Given the varibles while reading these pressures, is it likely this may be a developing area to investigate?

GM changed the criteria for compression tests on the V-blocks before the Y2K issue. You can do it cold. Throttle and choke wide open. All cylinders over 100 psi AND the lowest reading at least 85% of the max reading.

You are saying that a high pressure of, say... 140 max , must range at MOST, to a low of about 120 ? This is then acceptable? This also means dingharvey's numbers are ok, but low

140 * .85 = 119; 120 > 119 so I'd say OK.

for DNG's 120 * .85 = 102; 105 > 102 so OK.