50 hp 4cly 2 stroke failing under load.

[Firek4]

Hello everybody and thank you in advance for any help. I have a 50 hp, four-cylinder, two-stroke, mixed fuel and oil mercury, mariner outboard. It is mounted on a 13 foot mini powerboat, made by Saint Martin. It is a fiberglass v hull. The motor runs smoother than factory. we have changed every component on the motor and the compression on all four cylinders are approximately 125 and consistent. In the driveway with the ear muffs on, it revs and sounds great. The minute we put it in the water and throw it into gear, it does not rev very high and will not plane out.
HELP!!!!!!

 

[Droid]

You are not running on all 4 cylinders. Start with checking spark.

 

[Firek4]

Spark is good. All four comp good.

 

[racerone]

How did the motor run for you last season ?----Year / serial # ?----Does it have a belt driven magneto / distributor ?----Motor needs FOUR things to perform properly.----Good spark at the right time.----Crankcase compression.-----Correct amount of fuel.-----Compression in the cylinders.----Should not be hard to figure out what is missing .-----And list --" every component "---- here.

 

[Firek4]

I have been told that I may be over propped. It is an 11“ x 13“ pitch prop currently on there. The boat is new to me this year. I have checked everything top to bottom except for the prop because that’s what it came with. Could you recommend a smaller prop size and model number, if possible.

 

[racerone]

Have the actual output of motor tested.---Shops use a " test prop " or dynamometer.

 

[Firek4]

Will do! Thx