the Throttle on my Gravely 460 will not stay where I set it. If I push the throttle to wide open and start cutting in 10 seconds the throttle will move back causing the engine to lose rpm’s. It did it last year but this year has gotten much worse. I have to keep my hand on the throttle to keep it where it needs to be. The mower has about 1100 hours on it. I don’t know if a spring has gotten weak or if there is something wrong with the throttle cable although the throttle cable seems to move easily with no rough spots. Has anyone else had this problem and know how to fix it?