This motor should be under warranty. What does your dealer say?
If beyond warranty... Time for basic troubleshooting. 4-strokes go by the old race car mechanic's mantra... suck, squeeze, bang, blow. Those are the 4 strokes in most basic terminology. All 4 have to occur, and at the right time, for the motor to run.
What is your precise model?
First things to check are the very basics. Be sure the crankcase oil is not overfilled -- not even a drop. The crankcase only holds a pint and a half from completely dry. If you filled it with a whole quart, it is definitely over full.
Verify that the fuel supply is clean and fresh, and the primer bulb firms up when squeezing it. Run a water-separating filter if at all possible.
Does the motor stall at speed, or is it near idle? Is it only when cold, or only when warm?, or.. does it seem to be completely random? Do you get an oil LED indicator coming on as it is stalling? Does it POP from the carb when stalling? Are there any unusual sounds at all?
99% of all issues we have seen on these has been caused by the basics -- dirty or old fuel, overfilled oil, etc.