well i live in the part of texas where they sell stuff called Rocket Science Fuel, i allways ran 30 through my ws7-2[in the mbx5], but then i got my xxx-nt and i had to go down to 20 for that, so i started using the 20 iin the mbx5 too, seems weird but all i have to do was idle it down a little and lean the lowend a little 1/8th turn