That can be caused by many things.

1, Air leak in the fuel lines.
2, check your line in the tank, ( the clunk might be stuck forward or something)
3, make sure the carb is tight.
4, make sure you muffler is sealing
5, make sure the muffler nipple for pressure is not plugged
6, make sure the head is cleaned underneath and sealing (examine the shims)
7, check the highspeed needle o-ring might be worn out and is causing an air leak.
8, make sure the low speed is set correctly. If it is too rich it will load up and stall when you hit the throttle.. Adjust it so when you give it full throttle after idling it for a minute that it doesn't run dirty before revving up. Clockwise is lean, counterclockwise is rich( rich means more fuel).


try these things