I have a 2006 Rancher with a slip on HMF exhaust and a custom snorkel and I can feel that the air fuel mixture is off wack  im using the stock 128 main jet. If anyone knows what size jet i should be using. Please post me back if you have any idea.  

have you tried adjusting the fuel air mixture yourself?

is it cutting out or bogging down?

bogging down is a sign that the fuel mixture is too rich, cutting out is a sign that it is too lean.