1990 johnson 90hp lost power

[funfisher]

I have a 1990 model tracker pro series 90 H.P.Johnson ob. I've had it for two years and have never gotten more than 5100 rpm and 47mph out of it on a 16ft Nitro bass boat.Changed the plugs once (no improvement)replaced with Autolites identicle to what were in it. Have read a few tips and will change to Champion l77J4 if someone will advise if that is correct.<br /> Also last time on lake WOT seemed to run like 1/3 throttle. Wouldnt hardly come on plane. Any suggestions would be appreciated.

 

[Joe Reeves]

Re: 1990 johnson 90hp lost power

FunFisher..... 5500 rpm is the absolute top rated rpm of that 1990 90hp Johnson. You're obtaining a top rpm of 5100 and that's just about perfect. Any changes to the engine or prop selection will no doubt run the rpm over 5500, and that's inviting a thrown connecting rod. Not a good idea.<br /><br />Pertaining to the spark plugs, use Champion QL77JC4 or L77JC4 plugs with the gap set to .040 .<br />The "Q" indicates a resistor plug to help eliminate noise in any electronics you might have on board.