Yo . . . Young1 - The problem isn't the motor. The check valve/anti-siphon valve is on your fuel tank . . . NOT on your MOtta. They go to sh1t all the time.
If you don't have a check valve on the tank . . . then your vent (on the TANK)
is blocked.
I replaced my check valve with a regular 3/8" brass nipple . . . but the check valve provides you with some level of saftey if you're motor caught fire. Fire will supposedly only burn back to the check valve.