Check the gap in the carb neck it should be around 2mm.

Check hsn needle,is it to lean?Then it can cut the engine out on speed runs.

How are the temps?

Are you on breakin?

Do you run in cold temps?

Do you preheat the engine before starting up?

You can have a airleak on the engine,..........

Maybe put up some pics off the needle settings.

Give more info please!!