hello....I built myself a motorized bike using a HS 50cc 4 stroke, a 4g trans and a shifter kit from SBP....well I must say how happy I am with this set up......runs really well....I should note I have also changed out my air cleaner with the SBP cleaner.....as a result I have unscrewed the mixture screw to allow for more fuel...after a few test rides I have managed to get this thing purring like a kitten and running very smoothly at high speed...Idle has been set at 2000 rpm thanks to my tachometer...seems to run very evenly until today...I was going up a slight incline and running the bike hard 5th gear shifting to sixth gear at 7000 rpm, continued to climb the incline in sixth and reached the top and a stop sign. I gave the bike gas to continue on and it stalled immediately...I stopped on the side of the road and pull the engine cord and the bike fired up first pull but then began to climb in rpm from 2000 idle to 3 and 4000 rpm engagingal the clutch and then back down to 2000 rpm all on its own. 2000 rpm and then it would be okay for a few secs and then back up. I have read a few posts online suggesting this must be an air leak but you would think if i had a air leak the motor would run lean all the time not up and down like it is doing.....any suggestions would be great...also I tried closing my choke somewhat, the rpms drop down and the bike is ridable but there is a huge loss in power....thx