yamaha g1 chugs and sputters

[jeffo85]

I have what i think is a 79 or 80 yamaha g1. When the motor is cold just starting out the engine runs fine but when it warms up it takes off really well then chugs and sputters badly. Its got 135 lbs of compression, new gas. i was told about spraying carb cleaner around the crank seals to see if they are bad. i tried that and nothing changed with the motor running wise. i put a new throttle shaft in the carburetor because the old brass bushing was shot. I got a new coil coming. Just thought i would see what else i could do.