09-15-2011, 10:39 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?