check to see if the nylon bell shaped valve is seating on its base with a fully closed throttle.Stripping down my over revving G4 carby from the motor on 2 of my victas revealed the over revving carby valve not seating on the base of the unit. Have seen a spacer washer placed onto the inner spring to help seat the valve in another video. I shall try this or apply a stronger inner spring as you have already placed new seals on top and bottom crank ends. Much difficulty with the bottom seal as the crank has to be removed requiring a total strip down of the unit
Ziggy Ozzie
March 2012