I have an x300 that will start, but won't stay running without holding the choke. After reading numerous similar posts, I have replaced the fuel lines, fuel filter, fuel pump, and carburetor/gaskets. There is fresh gas in the tank. It will start normally, but as soon as I let off the choke, it runs for about 3 seconds then dies.

At this point, it seems like the only thing left is the governor mechanism maybe? Any thoughts?