that weber engine makes 140hp and for 5 seconds on full throttle it make 160hp so if it did not enough power it was not running right.
I have one in my snowmobile and it drives this 2 place snowmobile me and my wife and great adventures and great speed and power.
well I can guide you some of the solar power system run on 24 volt like the wind turbine and the likes of that but never in the amps you are needing probably the max you could find is 45 amps
regulator, other then that I can't help you.
but what if you use relays like a ford starter solenoid...