I'm still looking forward to the day when my dad re-does the top-end on his '77 AW250. First things first, it's got the wrong cylinder on it. For some reason I'm not sure of, it has a gigantic 1975 barrel, which has older porting. Maico apparently made a vast improvement on porting for the AW bikes in 1976.
Second, the piston is dented. This happened when he started messing with jetting and points as per the Maico manual, not realizing that his '77 cylinder (which was using at the time) had been ported beyond the factory's specifications by Wheelsmith to suit a professional motocross racer. Thus, the bike needed a different set-up from a stock '77, and this particular combination make the engine go out of control. It revved higher and higher and higher in the shop, even after he pressed the kill button and turned off the gas! It just kept revving and revving and revving until he thought the bike was going to explode and send shrapnel through the walls at 150mph. I'm not sure what happened next, either the weird harmonic or whatever finally allowed the bike to rev down and die, or it just flat-out seized. Either way, it left a small dent in the piston that's surely causing the bike to lose a little bit of power.
If he doesn't do it in the next few years, I might have to do it for him for his birthday or something.