how well does your fuel tank seal, normally it one of the above or, your fuel lid pops open for a sec, at revs this puts alot of air in the tank with the result that you just exsplained
mine did the same thing saturday in the B-mains and it was just a loose engine mount.....it stopped me from finishing my first race...bummer.....oh well I guess the time they close the track for maintenance in between then and race time I should've gone over every screw in my buggy.....now I know.....