Doesnt VP racing fuels make a gas specificly for thumpers?
U4
Used in stock and modified 4-stroke applications, as well as stock 2-strokes. Makes up to 6% more power than pump gas and any basic nonoxygenated racing fuel. Passes fuel rules for AMA amateur racing and is also perfect for club level racing, CCS, WERA and AFM.
• Color: Clear
• Motor Octane: 92
• Specific Gravity: .718 at 60° F
got it straight from http://www.vpracingfuels.com/vp_01_fuels.html?mgiToken=0C15B7C812685993C8