Could be a lot of things.
How did you figure out to tilt it to start? Thats a sign of water slopping around in the bottom of the tank. Check your fuel for water in the tank/line. Drain it all into a container and look for a blumpy glob rolling around at the bottom of the container. If there is one its water and you will want to drain the carb and tank. Water from the air condenses in a half empty tank and then settles to the bottom of the tank as a blob since it wont mix with gas and is heavier than gas. This means that the carb is getting globs of water along with the gas and causes starting issues and sputtery running. Always add Seafoam to your fuel supply and keep your tank topped off. The Seafoam helps to bond the water with the gas so it will burn. It also stops the buildup of ethanol based crud from clogging your carb.
