Re: Gravely Pro Master 300
It sounds like it's fuel related. The carburetor may not be getting enough fuel when you put any load on the engine. You may want to try running it with partial choke. If it runs better when engaging the mower deck, the carb. may need to be adjusted, or taken apart, and cleaned.
Other causes of fuel starvation would be debris in the fuel tank around the pick up, clogged fuel line, or perhaps the fuel pump itself.