I have seen a few posts on here about late 80's 4 cylinder 45-50 hp motors that have no top endor won't turn over 2000 rpm's. I posted to one topic with a customer with the same problem and after everything electrical and fuel related had been checked I found this guy's problem. He spent allot of time on an idle only lake, like 6 out of the 7 months he used it and for what ever reason I lossened up everything holding up the lower pan and removed the exhaust and water jacket cover over the exhaust, and there was the problem.....carbon. big chunks of carbon had formed and they fell down into the midsection which is shaped like a funnel and all these chunks had the hole at the bottom blocked off, thus not allowing exhaust to get out at W.O.T., the motor would idle fine because the exhaust would come out the idle relief ports under the rear of the pan. Been doing this stuff for more years than I care about, and this is a first for me. Hope this helps someone.
Hitman
Hitman