How do I turn off oil injector on PW80?

I just bought my son a used PW80. Fun bike for him as he is 10 and has never ridden a bike before. I'd like to turn off the oil injection system so we can run mixed gas. He races a two cycle kart and we always have left over gas when the race weekend is over. My question is, can we use this race gas in the PW80? It is race gas (I think it is VP110 we buy at the track). It's mixed with 8 oz of Burris racing oil per gallon. If anything, I'd think it would have more than enough oil in it..

Any input would be appreciated.

Does anyone know how to do this? Possibly I just run the resevoire until just before it is empty then start running the premixed stuff? Suggestions?