hey, you need a bigger exhaust tip! nah, seriously, what is your set up? is the engine fairly standard? what have you done to it?
sweet, i hope i can help, but i need a bit more information.

have u checked your coil? think about how hard it is working at 6000rpm it has to prouduce 6000 accurate sparks for each cylinder, thats 24,000 times that coil has had to build up
a field and prouduce a spark each minute, so and faults will show up here.

also what grade of fuel are you using? it could just simply be a case of the fuel not being up to the task, over here in NZ they change the properties in the fuel at the change of
season, more light fractions at winter to ease cold start ect...

sweet! have a good one.
choice from chris.