2007 PW50 Running lean/HOT

Just bought a 2007 PW50 for my daughter. Oil injector was disabled, mixing Yamalube @ 32:1. After riding for 15 or more mins, bike loses power and begins running very hot. It has substantial top end noise, but otherwise appears to be making adequate compression. The main jet appears to be stock @ #70. Plug is bright white, so I know we have a very lean condition. She is just beginning, so very little WOT, and a lot of 1/4 to 1/2 throttle usage. Should I go up a size or two on the main. The needle in the carb has only one groove, but I found a needle on fleabay which is advertised to be for this carburetor and has several grooves which allow clip/needle adjustment. Please post any ideas. Thanks in advance, Matt.

Classic lean condition / detonation. Did you clean the carb? Those little jets plug up easily.

Sounds like it is just a little lean since it takes a while to overheat. I would try a larger pilot jet in case the PO put one in too small. Check the air screw setting, also. Shouldn't need to change the main.

Forgot to add that the PO stated that the oil tank was cracked, and he began to premix the fuel. It does not appear that the oil pump/line was removed at the carburetor.

Could it be drawing air through the line and leaning the mixture?

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