Mercury 90 hp I need advice

[Shammy34]

Mercury 90 hp 1988

Runs amazing till 4000 rpm then starts to sputter and won't go faster. The other day we were trolling for quite some distance then took off and boat got up to 5000 rpm and ran 35 mph. It has never ran that well.

We have replaced all three carbs and the fuel pump. All fuel lines were replaced and emptied gas tank and refilled with new gas. Still can't get it up over 4000 rpm with out it cutting out. Have tried squeezing fuel bladder and is firm while running.

I was thinking about a voltage regulator

Any thoughts?

 

[Karmago]

First thing I would do is check the high speed timing advance setting.. You might have it set just slightly off, if it does pick up rpm to 4000 and sometimes to 5000 but most of time doesn't. Service manual would help through this procedure. There are complete service manuals available online for mercury motors, I'm not sure if allowed to post link here but for sure you will find one if you look for "mercury service boatinfo"