Hi, I'm interested in the idea behind what you're doing, but I think you're going about it wrong.
I don't know what engine you're using, but almost none of the small engines I know of operate efficiently at WOT, there's huge efficiency gains to be made by better control of your air fuel ratio and timing being optimized for the rpm and load, as opposed to trying to lose pumping efficiency by turning the motor on and off. The power required to crank the motor over and over again to start it can only be supplied by either a very large battery, or a system to recharge it while in motion. The large battery is a weight penalty, the generator system will be a huge drag.
The small engines are almost universally set up with timing optimized for partial load, and WOT being rich to improve performance. Fuel economy is mostly a secondary concern as it concerns small engines.
You would be far better off to design a simplistic EFI system to improve the burn and keep the air fuel ratio constant at stoichiometric, and a mechanism to advance the timing under light load and retard it at WOT. I'm quite confident that the efficiency improvement, while using throttle to maintain speed, rather than start/stop would be much higher.
Of course, all the above is just my opinion. I do have many years of experience with motors, economy improvement modifications and so on.