carb flooding

i have a big 4wheeldrive 3/4 ton chevy truck lifted big tires ect. i have had my 400ex loaded in it before and had no problem with the ex starting when i unload it. but the last 3 days. i turn the gas off and try to start it after it ridding in the back of my truck and it is totally FLOODED i had to pull it for a 3/4 a mile before it got cleaned out and wanted to run.

any ideas why this happens or has anybody had this problem?
it just started occuring.
it doesnt bog out or accelerate werid it runs like a bat outta **** when it starts.
float bad? float valve bad? bad gas?
any ideas really need help and have no clue

thanks

Too Loud Too Bad

2000 400ex dyno jet kit k&n filter and outerwears, shark jaws bumper, rebel seat cover, no spark arrester 909 grips and 16tooth front sprocket

1975 4x4 chevy 33x12.5

[SUPERFLY 400]

The only thing I can think of is that your fuel shut off is leaking fuel into your carb even though its shut off. Which is no big deal, However, if your truck has a stiff suspension, the bumps etc. could bounce your float up and down allowing way to much fuel to flow into your carb. I had a 85 chevy with 39" swampers and it rode stiff, infact it cracked the frame at the rear shock mounting brackets.
I may be wrong, but just an educated guess;)

[Wheelie]

Check your carb overflow vent, when you stand your quad on end, the carb should piss fuel onto the ground. If the vent is plugged or not working properly, the fuel will go into the air filter, causing flooding.