Ive got one of tom's DR2 variators. It seemed good in theory to me but as of yet haven't had the opportunity to try it.
There's not a whole lot you can do to lower the power band in the howet. The Low end torque in a howet is about as good as it gets in a gy6 due to the internal gear ratio. 13/42 gears for a ratio of 3.2 to 1.
There are few things you can do to help lower the power band. one is a torque exhaust pipe, a small diameter 3/4 to 7/8 inner diameter pipe about 30 " inches long will help low end but hurts above 7,500 rpm. you will loose power on the top.
Going to stiffer (red) springs in the clutch will raise the engagement rpms which will put you closer to the power band at take off. gives a real snappy take off but your axle, chain and sprockets will take a beating! Like reving a car to 5 grand then side stepping the clutch. Not the best choice for casual riding.
A 30 MM pumper carb will definatly give more punch at takeoff but you will have to swap the head and intake to 30 MM port sizes. you can use this carb on a stock 24 MM head but it may be a pain to get the carb tuned properly. The stock howet head ports can take the extra flow but the 24mm port openings will cause a loss of the full potential of a pumper carb.
I have always used synthetic oils except when breaking in a new set of rings. Honda makes a synthetic oil designed for air cooled 4 strokes that works very well but pricey.This oil handles the high heat of air cooled heads without breaking down. Any synthetic had at the local auto parts will work, but you can't go all season without an oil change. about 10/12 hours of ride time is all the oil can handle before heat starts to have an effect on the oil.. Most oils can't handle heat continualy above 275 f. without breaking down. Head temps in a gy6 can reach 350 f. easy.
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