I got rid of most of the vibrations on my bike and i can cruise at 30mph, thats fast enough for me on a bike. I weight 125lbs on a 26" cruiser bike with a 48cc engine and
44t sprocket. If you want to go a little faster you could get a smaller rear sprocket. I prefer my 44t cause i dont have to peddal not even to take off. I switched my rear coaster break wheel with a mountain bike wheel(still using wide cruiser tire). and i switch my front cruiser fork for a mountainbike fork with shocks and front brakes(brakes work great).
I tryed that not using the peddles thing and my clutch pads lasted a good month if that.