You can't use a standard throttle on a Powabyke because they work on reverse voltage. 1.2v for full throttle and 3.8v for zero throttle instead of 1.2v for zero throttle. Also, IIRC, you have to pedal before the throttle will work. There's a 2-position switch. In one position, the throttle works after you've pedalled once. In the other position, you need to pedal all the time for it to work.
If you pedal along, open up the throttle fully, then when you let go, you'll get full power, so be careful because the throttle will work in reverse. Controllers don't normally allow power until they've seen a zero throttle condition. That's a safety feature and why you have to open the throttle fully before it works