Merc 150 Power Surge

[dannyboy7]

I have a Mercury Mariner Magnum 150, 1987 with plenty of hours on it. I was given a new Prop with purchase of 1987 Stratos 179 SC boat, and put it on. 3 Blade 21 pitch, SST. Spun it with the first outing as it was made for Yamaha. Replaced prop with reconditioned prop from prop specialist and same issue with nut backing off slightly. I have about a 1/16 movement from back to front on spindle. Issue is I go to plane, the motor will bog down or rev real high, and never the same. After under way, it purs along nicely, with a few surges. i am puzzled by inconsistancy and want to know if it might be the motor that is going. RPM at 3/4 throttle is 6000, and have not tried to find a higher range. Best speed prior to spedo's death was 55MPH. Boat has a Pro Hi Jacker plate with it raised 1 inch. Trim works, but I seem to wind out the motor with anything past 1/4 up. I was getting serious Chine or bobbing due to power surge. What should I do?

 

[studlymandingo]

Re: Merc 150 Power Surge

I don't think your motor is "going", it's probably just broken-in well. Check your compression, all cylinders should be within 10% of one another.

Surging sounds a bit more like a fuel issue, perhaps a tiny hole in a line, or a fuel pump with a tiny hole.

 

[dannyboy7]

Re: Merc 150 Power Surge

I had the compression checked prior to purchasing and they were all low, but within 10%. Should I be concerned with fuel mixture? I am relying on the original oil injector, and having thoughts that the previous owner might have had the same issues. On test ride, owner admitted to fuel being rich due to mixing oil in the tank on top of having the injector.....I replaced the line from the tank to the motor, but will check the pump. Thanks for the response!

 

[JB]

Re: Merc 150 Power Surge

Sounds to me like you are ventilating the prop. That can cause it to spin when it grabs water again.

Drop the engine an inch or so and see what happens.

 

[spdclp]

Re: Merc 150 Power Surge

I would lean towards JB's response.
We had that issue once and dropping it a "notch" helped.