Try this:

1 Loosen the screws that hold the carb in place

2 Press down on the carb so it is tight against the crankcase

3 while holding this pressure, re-tighten the bolts.

If that doesn't help, do this:

1 Remove the Low End Limiter collar

2 open the throttle 1mm

3 Close the low end needle

4 open the low end needle 1 1/5 (One and One Fifth) turns (this is where it is SUPPOSED to be set at the factory, but a few slipped by with different settings)

5 replace the Low End Limiter Collar.