firecrackers, firecrackers! light the fuse on that one and let it go. 150cc performance just isn't made to go 70 mph reliably. step up to a maxi scooter. 250cc or larger. Maybe a motorcycle. most reliably are the Japaneese brands, Honda Suzuki etc.
Anytime you burn the candle at both ends, it burns twice as bright. Also twice as fast.