A little Help with Engine modifications

I was wondering how / if you can modify a engines power.
As its stands. I’m currently confused to as a few numbers I am getting with a motorcycle I made.

I own 2 motorcycles, a 600cc, and a 1463cc respectively. I found a V-twin engine. I got a saddle, I got 2 motorcycle wheels. Cobbled it together. Weights 360 odd lbs and it only has a “safe” speed of 37 with a max of 78 (risking engine damage) or so mph… without cargo. I’m not against editing .json files just need to be pointed in the right direction towards what one modifies the power the engine outputs.

As for a 1.0l vtwin going only 38 mph on a 300lbs or so frame is quite humorous because my 600cc goes 110mph and weights in 543 lbs without rider. My 1463cc goes about 150+ mph without much problem. 0-60 in around 3 seconds… and it weights a behemoth 743lbs. (RL stuff.)

Thanks for reading… hopefully a few edits can get my vtwin pumping at least 100mph out of such a light frame…