I'm with you D I Y, I'd go two stroke 100cc.... but ONLY if he's a good mechanic. We know they are fragile.
I'd suggest almost any 100cc motor Parilla, TKM (preferably NOT the BT82 as they will cost you more and are not the fastest motors), Rotax (not the 125 Rotax Max motor!) Sirio, Hewland Arrows, etc, etc.
The trick to making them cheap and reliable is to keep the revs LOWER (run a too larger rear sprocket). Some of the 100cc motors were run around 20,000 rpm (and I once saw a 'works team' motor run to 22,000....). High revs shorten the life of the motor.
In full race trim, and run at 'race revs' these things have a rebuild time of ..... EIGHT HOURS MAXIMUM..... but... if you take 1000rpm of it's design limit, that will give you 16 hours running, a further 1000 of will double it again to 32 hours and so on. Yes.... you won't get the out and out performance but you WILL improve the life expectancy.
Two strokes either use Rotary Valve or Reed Valve for maximum performance. However, engine with carbs feeding directly into the barrel (not the crank case) such as the TKM BT82 are available but, usually, they are not es quick so... stick to Reed or Rotary.
When you find something, tell us what it is, get it checked over and ask your tuner the max revs for this motor.... then drop that range by about 2000 rpm and save your pennies!
Ian
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