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View Full Version : Merc 454/340 loss of rpm 400



swws11
09-15-2011, 09:39 PM
I have a 1987 Merc 454 / 340 with about 500 hrs. I have slowly lost 400 rpm over a few years, had tuneup done plugs, cap & rotor. Have done compression check on engine cold all cylinders at 125 psi. give or take 1 or 2 degrees. Any ideas why loss of rpm?
Thanks