There is obviously a bit of confusion, and difference of opinion here. We need to agree on this , to help the guy get his bike back on the road. I have some background in practical and theoretical electronics, but I am open to correction, and I do not know everything. When we talk about a 35 amp controller, what exactly do we mean? Do we mean that the controller will shut itself down when we try to put more than 35 amps through it?.
As I understand it, a controller works by pulse width modulation. So it is basically a switch, which switches the motor on and off at a very rapid rate. At a low throttle setting, the switch spends more time off than on . As we open the throttle more, the "on" pulses get longer than the off ones. Finally, at full throttle, the motor is switched on at all times, and there are no off pulses.
So at full throttle, the controller plays little part in the circuit, apart from acting as a closed switch. So at this point, the current draw is determined only by the battery voltage , the motor resistance, the motor back EMF, and any resistance in the battery and wiring. So at this point we could replace the controller with a bit of wire, with no damage to the battery or motor except that the motor would run at full speed all the time .
So if I am right [and please tell me if I am wrong] You could fit a controller rated at 1000 amps and it would work without damaging motor or battery.
REMEMBER THAT IT IS IMPOSSIBLE TO DRAW MORE THAN 20 AMPS FROM THE BATTERY AS IT HAS A 20 AMP FUSE.
That is my opinion, but we desperately need other opinions.
One way out would be to do exactly what Stimil has done, as his bike seems to be working without any problems.