Re: bmx w/Yamaha 100
check out the pirelli ML 75 moped tires. they're 2 1/2 x 16 and fit on 20" bmx rims. they're reinforced and have a J speed rating.
i bought mine new for 17 bucks each.
last long, streetbike tread and grip awesome.
not exactly a bmx tread, but you don't exactly have a bmx bike anymore.
but if you want to keep it bmx, check out maxxis hookworms or kenda kiniptions. both grippy, long lasting tires (long lasting on a bicycle, that is.)
whichever way you go, get some heavy duty tubes.
i also wouldn't recommend solid tires. i've popped them off bicycles before, or spun them on the rims just from pedaling. they're mostly used on cheap kids bikes and trikes where they don't get abused. they have no give, no traction, and, well, suck...