Mid Range Engine Problems

[Half Fast 623]

I've recently repowered my 25' Celebrity with a 1999 Mercury Optimax 225 from a 1994 Mariner 225. As I throttle up, the engine runs great at idle and lower speeds, but as I move the throttle forward slowly and reach mid-range it shakes, runs unevenly, and won't go any faster. I can move it slowly up to full throttle and it stays caught it mid-range. However, if I start in neutral and jam the throttle all the way to full, it runs normally at full throttle.

I tested the throttle cables and they appear to be working fine. The Mercury tech tested the engine and no issues were detected. I don't know what could be causing the problem. Any ideas?

 

[CharlieB]

Re: Mid Range Engine Problems

I'd start by putting a gauge on the fuel line to verify fuel pressure at the regulator, it may be sticking as the throttle is slowly opened yet work fine at sudden extreme movement.

What did you do with your old 225?

 

[Half Fast 623]

Re: Mid Range Engine Problems

Thanks. I'll try that. I just gave my old Mariner to the tech that installed my new one. It was 14 years old and barely made it to the boat ramp.