If you are running pump gas in this motor then I would not redrill any of the jet holes in this carb. Look at everything else before you start changing the jet sizes. Double check the ignition wiring first, neg. coil wire goes to points, pos. wire to battery. Check for valve leakage, turn motor over by hand and listen to exhaust and intake openings for a slight hissing sound. Check float to make sure it has not gone bad, I have seen many Kohler floats start leaking at the solder joint on the float. Like was said earlier in this post, when adjusting for a mower or service application turn the motor to operating speed which is 3600 rpm, before adjusting the top/main jet. If it is a race motor then hold it wide open when adjusting the top/main jet, (just don't hold it wide open for too long!!). If you have the idle too fat it will overload the top end circuit, and will still idle OK. Adjust the idle screw clockwise until it starves for fuel then back it out a little, this will keep this from overloading the high speed circuit. Make sure your vent holes for the boal and main jet are not plugged. make sure there is not too much slop in the buterfly shaft and it is not sucking air through the shaft. If you start drilling out the jet and you are running pump gas or race gas you will overjet the carb, and will have even more trouble adjusting the carb.