Thanks for all the help.
I rechecked the carburetor float, made adjustments as per manual etc; all was fine.
I checked the gasoline flow to the Carburetor and was only getting a trickle. I removed the bowl and it was filled with a kind of slime. I cleaned it and blew out the fuel line. Put it back together and the tractor runs great. I only had to make a small adjustment to the main carburetor screw.