My mechanic cannot figure it out!

[Hookin_Hogs]

Okay this is going to be a rant so I will try to include all I can. First off I am running a 1998 Mercury 150 XR6 on a 18ct fiberglass boat with a 21p prop. What it is doing is when I push my hot foot to the floor to hullshot it bogs down unless I let off and slowly go to top RPM (5400-5500) and then it goes all day unless I come back down to plane again then it’s the same story. Yet when I am at WOT and I let off if I am still at plane(ish) 30-40mph and I push the hot foot down there are no issues. Here is what I have done so far. Carb rebuilt and sync n linked, throttle, oil injection, and timing have all been checked and set. New fuel lines all the way around to insure no fuel leaks (that I know of), new fuel pump, new impeller, new plugs, and I’m sure I’m forgetting something. Not really sure we’re to go next, my idea is maybe the carbon is built up heavily in the exhaust port therefore not letting it breath properly only say this because if I put it in reverse and I get water bouncing against the motor it dies. Any input would be great and I will answer any questions needed. Thanks

 

[racerone]

Did this problem develop suddenly ?------Compression checked ?------Sound like the idle mixture is lean.----To test that theory you push the key in momentarily before the holeshot attempt.----Should be easy to figger this out..

 

[Faztbullet]

Is the exhaust relief buried?