procoater

I have a 1996 zxi 1100, this will be my second summer running (owning) it. Last summer i took it out and it ran great for our 3 hour trip on the lake, then every time after that it would lose power and only rev half the rpms even at full throttle. So here is a list of things i have checked or done to fix this issue, all the tests were done per the manual.
1) checked temp. sensor, good
2) checked comp. in all cylinders, good
3) changed fuel filter
4) removed and cleaned out fuel sender
5) removed each coil and ran on a tester ,all are good
6) replaced plug wires and boots
7) made sure all water lines and fuel lines are clear
8) removed carbs and inspected the internals, look like new, no grime
9) cleaned out tank vent, works well
After all of this, we took it out two weeks ago and it ran awesome even with a passenger for at least two full hours, i figured it was finally fixed after all that i did between then and now. Well we took it back out and then it was acting up again, no power, smell of fuel, and i would have to sit at idle for a little while just to be able to move back to the loading ramp, sometimes it would give me a nice full throttle pull but not for long.
The oil system is removed so i pre-mix, was told 44:1, i just changed the plugs and they were a light brown color, not white and not black or gummed up, but i changed them anyway, i haven't been to the lake yet to see if it was the plugs yet.

Any ideas... similar problems? Please help. This thing is bugging me. I want to be able to enjoy it without worrying all the time.