I have a new LT that I purchased a couple months ago from a private seller. Its a 6.5 HP gx200 longtail that had only been started but not ran in water when I purchased it. It sat from January 2011 to July 2011 and was not winterized. The motor started and ran well the first couple times out. Recently it has been cutting off under power, usually when i'm at full throttle the motor just boggs down. First time it happened I restarted it right away with no problems. Last time I let it sit before restarting and it wouldn't start. It will go at full throttle out of the water but boggs down at full throttle when underwater pushing weight. What could be the problem?

Clean the carb

Well I got the tank 1/4 full and put "extreme" the cleaner gas from the gas station and put that in there. It went through the first tank fine. Then I fill the whole tank with the cleaner gas and this problem occurred while going through that tank.

Or check ur spark plug an wire

Your coil may be going out.

A new coil, plug wire, and boot is about 30 bucks.

Clean ur carb real good ditch that fancy ass gas
Sea foam is thd best cleaner I've found

yea some times those metal tanks will rust and clog the carb. clean carb and use an inline filter for gravity fed carbs.

My brother and I build small longtails and I would be willing to bet that if your motor continues to start and run when not under load that its not a motor problem. Depending on what size prop you have and load you are pushing your motor may need the cavitation plate adjusted so that its not running too deep. If its running too deep its killing the motor because it doesn't have the torque being a 6.5 hp motor. Bend the cavitation plate down towards the prop to create lift and get the prop closer to the surface. This may fix your problem. Good luck.

My guess is bad gas. I've had the same problem when water gets in the gas...