Do you live in an area where the mower isn't cranked during winter months ? And, did you leave fuel in the carb during this period ?
Internal combustion engines crank up based on vapors, but the new EPA gas has VERY low vapor content. So your carb insides MUST stay immaculately clean, but storing with fuel in the system for prolonged periods (like over winter) can leave all sorts of
MUCK which can/will close off fuel passages.... like the jets used for starting !!
Since your mower is still able to run, you might try a "fuel system cleaner" (such as
StarTron) or running high test name-brand,
Top Tier fuels with the built-in cleaners (such as Chevron or Shell).
Article Here. Try this for the remainder of the mowing season, otherwise it's visit your local mechanic time.