I'm a noob here and I just mounted a 66cc skyhawk motor and put it on my mountain bike. I was just wondering if riding on mountain bike trails would cause any damage to the engine.
Provided it's properly installed & maintained - no, no damage at all from trail riding, I do it myself quite a bit actually... you may find an occasional response lag as sometimes during the roughest bits the fuel gets agitated & the bowl hasn't filled properly, but that's rare & only one of my bikes does that (NT carb).
You also may find the stock 44t sprocket too tall for the technical, tricky bits on the trails... but ofc I just pedal those