I believe that your motor has carbs and not EFI. Correct me if I'm wrong. But if it does have carbs, sometimes junk will get in the bowl and block the jets. When you pump the bulb it will force the fuel in, but not if the junk settles. You might also check to see if you have a check valve in your tank, some tanks have them some do not. Might not be sealing
and letting the fuel back in the tank. Good luck..