2002 2 stroke xlt800 great out of the hole then bogs ? Winterization - carb diaphrams

[Warlock003]

Hello I did the same winterization to the craft in the fall of 2011 that I did in 2010. I only left about 5 gallons in the craft but put in lots of Startron fuel treatment.
Summer of 2011 craft ran fine.
Summer of 2012 great out of the hole for 100 yards then barley idles and shakes does not die. If you wait 30 seconds - one minute it will go like a banshee for 100 yards then same thing. I am able to maintain a low to medium speed say 26-30 MPH probably all day but the minute I open it up wide open throttle it dies.
Here is what has been done so far:

I replaced and verified spark plug gap.
Battery is brand new and starts the craft and cranks lots so battery seems good.
Plenty of thrust so grate seems clean.
No overheating (no de-rating of computer ignition)
Replaced fuel filter (simple cheap paper filter under glove box)
Fuel tank vent line was full of a water and gas mixture. I rained the bowl thing in the extreme front of the craft and sucked and blew thru vent it seems ok.

I am thinking either water in fuel from first fill up at a gas station so I may remove all the gas and place know good gas into craft.

Remove and clean and rebuild carbs.

Last question do you need to do the pop off teat every time or can a homeowner / somewhat qualified backyard mechanic like me rebuild carbs and by pass the pop off thing ?

Thank you Eddie.