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I have a 1987 140hp V4 that has 100 psi compression in #1 cylinder and 115 psi in 2,3,4 cylinders.I took off the head to check it out and found a slight groove in the cylinder thats most likely the reason.It would run okay on the hose,but when I put the boat in the water it stalls when put in gear...Even with the compression issue I would think it would still run half way decent...Any input besides what I already know? Its on a 1988 C-Hawk 22 ft pilothouse and I leaning towards a new motor after I replace the deck and fuel tank.
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Assuming your lower unit is okay....................
The 15 lbs difference in the compression psi would not cause the stalling when engaging a gear, either forward or reverse.
Spark plugs should be Champion QL77JC4 plugs gaped at either .030 (long life) or .040 (strong spark).
On a flushette, the idle on a 20" shaft engine should be set to 1000 rpm.... On a 25" shaft engine= 1200 rpm. If you're undecided as to which shaft engine you have, measure from the underside of the transom bracket (the bracket that normally sits on top the transom) down to the cavitation plate just above the propeller. Whatever measurement you come close to... that's it! In the water... the idle rpm will drop to normal.
With all spark plugs removed, check the spark with a tester whereas you can set a air gap of 7/16" (important). The spark should jump that gap with a strong blue lightning like flame... a real SNAP! Does it?
If the spark is as it should be. in all probability, your problem is due to either the idle rpm is set too low... OR... carburetor fouling that will cause at least one cylinder to run lean, which leads to cylinder wall scoring and a drop in the compression which you've already encountered.... in which case, it is advisable to remove, clean, and rebuild the carburetors as needed, using complete kits.
The high speed jets which can be found horizontal position in the bottom center portion of the carburetor float chambers should be carefully cleaned with a piece of single strand wire as solvent just doesn't do that job properly.
Let us know what you find.
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