The best way to increase performance??
Unload all the un-needed stuff.
Built in tank? Only run 1/2 tank.
Add trim/***.
The motor could be bored out but the results aren't really noticeable.
Unless you go .040 over and re-jet.
The intake ports and exhaust port could be shaved and polished for smoother flow.
The older 75 is pretty good just like it is.
The 75 was rated at the prop and was more like an 80.
The newer 90 is rated at the crank and more like an 85.
The very best way?? Buy a bigger motor.
They sell used 125's fairly cheap.
Depending on yours and their locations.
Changing brands will be a lot harder to swap over .
The Chrysler/ Force would be an easy swap.
The differance between the 3 cyl. 75Hp and 3 cyl. 90Hp are larger intake ports and larger jets in the carbs in the 90Hp.
Earlier in the begining of the 70.es there was a 70Hp and a 85Hp 3 cyl. engine.
There difference was the same, lager intake ports and jets.
The lager engine had a 13x17" prop and the smaller a 13x15" prop, but the same gear ratio.
