Re: The Pocket Bike Engine and Your Opinion...
Re: Gripshift as throttle input. It can work easily enough. Carefully remove the rubber stationary grip (air compressor or rubbing alcohol and twist off). Loosen the gripshift retaining screw (small allen bolt under the grip).
Slide the gripshift off the bike. On the outer end of the shifter will be a plastic ring cap held on by 2 or 4 plastic tabs. Carefully lever them loose with a flat screwdriver, so the two shifter halves come apart (stationary part and rotating part covered in rubber grip).
A small S shaped metal spring will fall out. Retain this if you wish to use it as a gripshifter ever again, or have notched throttle control (use the 8 speed side, not 3).
Lubricate and re assemlbe the shifter without the s-shaped spring. You will need a heavy return spring at the other end of the throttle cable. It has to keep constant tension on the shifter cable or the cable end will pop out of the shfiter housing, possibly causing a loss of throttle control. Good luck.