It has a new filter and elec pump on it, with all new rubber hoses. Maybe the metal hose got some #### in it. Ill blow it out with a air gun tomorro. I might re-loacte the pump too. It says in the manual the optimum position is neer the bottom of the fuel tank but must be within 1 foot of the bottom of it. I have it in the engine bay and from my rough measuring it should be within a foot (on the top horn mount).

How does a lean mixture make it backfire thru the carb? I havnt seen it spit any flames out, just raw fuel.