My buddy has a Polaris 50 Scrabbler for his kid. He wanted to get a little more power out of it. He took a little ring out that was restricting air from where the exhaust connects to the head and the bike has a lot better bottom end now. But now the bike cuts out at half throttle to full throttle. Does in sound like the jet needs to be a little bigger and is it possible to get different size jets for this type of bike?

Removeing the restrictor on the exhaust is step 1 Then;
Removeing the OTHER restrictor in the air inlet to the engine is step 2.

The owners manual will show you how, or swing by the dealer and they should show you gratis.