OK, OK, I get it. I am not fit to say I"m a tennis player.
Fast Freddy. I had the last of the aircoolers and the first of the following year watercoolers. Simple fact, air coolers were lighter by about 10-15 lbs., had the same power at the beginning, lost a bit of power, maybe 15%, after 10 minutes. Most motos barely lasted 15 minutes until you make Expert, then it might last 20 minutes until you enter a pro outdoor, but by then, you're shop or factory sponsored, and everyone is getting tired.
I"m a lightweight, raced 3 Novice 250 AMA races on my brother's 250 Honda 4 stroke kit'ed by Champion, using a Champion frame with Cerianis, and Koni's, way back in '78. Mid pack starts, lots more control, hole shots in muddy conditions, but lack of power compared to two strokes. It only had 8" travel, front and rear, so was giving up some performance in whoops, gaining some in the turns. All 3 races at Dixon's ArgyllPark, few whoops, lots of doubles, sweeping turns and fast straightways. My '77 YZ, bought from an expert, had 12" travel and almost the power, it was a 125.
I like the four strokeYZ's-426 for general goof around riding, but maybe not for racing Open class. I need something with a lower center of gravity, so would pick a torque oriented 2 stroke of around that size motor.
Some riding style work better with powerful 4 strokes, while other's prefer a lighter weight, better turning bike.