Clean out the vent hole in the fuel tank cap. It is likely clogged and as the fuel in tank is depleted, a partial vacuum forms, making it difficult for the engine to get sufficient fuel. If you want, run the engine til it begins to show the symptoms, then loosen the gas tank cap and reseal it. That will break the vacuum and the engine will immediately respond and run better.......until the vacuum forms again. If loosening the cap improves things, probe the vent holes on the cap (inside and outside) and if you have compressed air, blow out the cap with it.

Thanks, mownie!! I found the three little holes. It amazing now shes purring like a kitty and with the throttle adjustment that it needed shes got a little more ummphh!

blades will not start when I pull the engagement knob
all the pulleys move manually but nothing happens when I pull the knob?
thanks