03 yamaha 15hp 2 stroke problem

[yamaha15hp]

I have 03 2 stroke 15hp yamaha on a 1452 polarkraft thats having problems our local guy cant figure it out! It wont run under a load in the water like 5mph. We have put a new carb on it, new fuel pump, new sparkplugs, new fuel filter, new gasline with a fuel filter on it going to the motor, new gas the compression on both cylinders is great the voltage going to the spark plugs is 280. We are stumped what else could it be? If you could help id very apperciate it.

[99yam40]

to run properly a motor needs
1.good compression(what numbers did you get),
2.good spark( is this 280 the peak voltage to the primary of the coils and is it on both?),
3.correct timing( did you check it at both idle and WOT? and did you make sure of what it was while problem was occurring?
some motors retard timing while in safe mode from over heat or oil level problems. Does your alarm system funtion properly?),
4.and the proper fuel/air mix

If the compression,spark, and timing are good then you are left with fuel problems.
I take it you replaced these things a little at a time and while doing that maybe some trash or water ended up in places that are causing you problems still