Opinion on what engine to buy for my dirt bike?

So i got an ssr 70-c its really small, im 14, and 5'6, i raised the rear suspension with thick washers, and bought a gripper seat to make it 3 inches taller, so anyway i am gonna buy a bigger engine since i dont really wanna get a bigger bike altogether, i like this one it has pegs and a wheelie bar and i pop wheelies on it, so anyway i narrowed it down to 3 possible engines the lifan 125, 140 , or 150, i got a $550 budget but i would prefer not to spend all of it since ill be saving up for a street bike soon :) , so anyway, ive ridden my friends dirt bike, it has a lifan 125 in it he paid $300 for it with the set of carb wiring etc, i dont mind buying it but i want something bigger, id buy a 140 or 150 but then i need to pay more for an oil cooler and the wiring :(

My big question is, is there any 140cc or 150cc engine out there that is air cooled?

And can you guys give me the names of some other engines, my ssr 70-c is a honda crf50 clone, so any engine that says "a bolt in replacement for a crf/xr50" will fit on my big.