I have a 98 merc 45hp (60 hp powerhead) jet outboard that is having issues. It is on a 16 ft alumacraft flat bottom. Last week i had it out and it Worked perfectly. Good hole shot, smooth top end, no rpm meter but around 28 mph.
The other day I had it out and it was having a hard time getting on plane and it would run 22-24 mph top end. After running for a while it would die. So, I put in a new fuel line; new tank; rebuilt the fuel pump; and now doesn't die after a few minutes of running WOT. It still doesn't reach the correct top speed and has a poor hole shot, sometimes.
Crazy thing now is that it runs perfectly 30% of the time but the other 70% it does not. When two people are in the boat it seems to run better (I adjusted the trim of the jet but didn't help). Also, when I turn sharply, the motor rpm's dive. It doesn't kill the engine but it cuts out until you turn the motor back. I checked for kinks in the fuel line, nothing. I even mess with all the lines going into the motor when it is running straight and it does nothing.
I am wondering if there is a rev limiter on the engine or if I may have an issue with the float in the carbs. Any insight???
Then look for electrical issues, coils, frayed wires, loose connections, switch box, timing advance sticking, etc. It can be hard to tell when it is only intermitent, you have to catch it when its failing.
Anything is possible, but I haven't seen a rev limiter (the one for max RPMs) cause this problem (I'm sure it has though). Some motors have a slow mode, if the motor gets too hot, or is not getting enough oil, it can limit the RPMs to help prevent damage, I'm not sure if this motor has this feature or not.