The engine will run best with the HH carb needle on the 2nd clip postion and a 122-125 main jet and stock pilot jet. 30-1 oil ratio is required for this design engine, or failures will occur. There is too much open space area in the crankcases as the reed valve is too far from the crankshaft in this old design engine. Stock gearing will work fine for heavier riders and lighter riders can use a 15 engine sprocket. The bike handles better when the rear is lowered 15mm. The bike suffers from bad brakes. This is the fastest 85cc bike to race, but it requires the most upkeep, and its also the lightest engine and gearbox. Best mods are HGS or VH special exhaust, VHM head and carby boring. faster riders need to mod the clutch as they slip to much. Swingarm and Fork extentions work well for big wheel riders.
General problems- running more oil is required, fast clutch wear and slippage, fork seals leak easy, throttle cable problems and the brakes can be a constant problem.
Race fuel works well. Porting work adds power. Good parts supplies in Australia.