I have a Husqvarna Yta 22v46 Model - 960430212 Series - 030816A003570 it’s approximately a 2018 year model. It runs on idle but when you incrase increase speed It starts surging but will not increase the RPMs/power. It also seems to spit fuel out of the carb. I’ve had the mower at a repair shop for six months and he’s not been able to figure out what the problem is anybody have any suggestions?