This just started when i went back to mowing pasture. I set throttle at about 75% to mow but it keeps kicking it back to idle even if I don't have a load on the mower.
IH Farmall 656 gas/ IH 240 Utility/ 2, Super C Farmalls/ 2, Farmall A's/ Farmall BN/McCormick-Deering OS-6/McCormick-Deering O-4/ '36 Farmall F-12/ 480 Case hoe. '65 Ford 2000 3 cyl., 4 spd. w/3 spd Aux. Trans
It sounds like the friction disc, at the bottom of the hand throttle assy., that keeps the throttle in place is worn/deteriorated, and needs replaced, or adjusted as mentioned. I have made them from heavy gasket material, like 1/8" thick to make new one's, and will last a good while. Replacement disc appear to be made of sheet cork gasket.
Here is a link to an aftermarket disc to give you an idea what it looks like. Throttle Friction Disc