What is causing my 04 merc. 50 4str efi to max out at 3200 rpm?

Question

History-last year motor running fine-during winter storage maintenance I cross-threaded a spark plug hole. Brought it to a Merc. service center, head was removed and heli-coil installed.

I got boat back from mechanic with a bouncy idle 800-820rpm, mechanic said possibility bad gas-Used Stab-il when I did storage maintenance? Also motor shakes/vibrates causing steering to turn at idle because of bouncy idle.

I finally got the boat out yesterday, first time all year-the it would not go past 3200 rpm-all out-very under powered.

In reverse the Rpms go past 3200. I put fresh gas in yesterday morning-premium.

Answer 1

OK, first get rid of the premium fuel.  All merc 4/s are designed for 87 octane, up to 10% ethanol.  This could be a number of things, i would start by checking the valve timing, could be out a tooth.  There are alignment marks on the flywheel and the cam pulley.  If this is a fuel problem, the only way to diagnose it is by having the motor scanned by a dealer, which should have been done in the first place.  Our marina "hooks up" every EFI motor, firstly to check operating hours, and to verify serial#s.  And of course, check for water in the fuel!