vacuum test 225 HP Mercury Offfshore

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can you perform a vacuum test like where the fuel pump connects to the block to tell if the crankshaft seals, reed valves,and cylinder rings, are sitting right without to much wear, like the way you would test the lower unit, and if so what would be the precentage of vacuum leakage allowable. I have a 225 HP Mercury Offshore and after about an hour running the engine will running at full throtle it runs good but really bad at lower RPM and I wonder if a worn engine if low vacuum would cause the fuel pump not to supply the proper amount of fuel Thanks Bob I am thinking of going to a electric fuel pump