Welcome to the forum! So have you confirmed that by engaging the switch that it is cutting spark? I mention this as if the PTO pulley isn't able to turn, it would snub the engine. Or if this is too lean, a partial choke may help this run up. If yours has the RIO (reverse interlock operating switch), try pushing that in when engaging the PTO. Or some are in the PTO switch themselves- when pulled momentarily fully out. Electrically, safety circuits run through the PTO switch. I don't think that I have anything digital on these, but I will look.