Originally Posted by atv connection

It sounds to us like one of two issues: Electrical or carburetor jetting. We’ll begin with the more likely of the two, the jetting. It sounds to us that the machine is running lean. Since you said this was an ATV restoration project, have you made certain when rebuilding the carb to jet for your area’s elevation and to accommodate for any modifications you performed in the process? You did note having performed a cylinder bore, which can often demand jetting changes. Other mods that would certainly demand larger jets are the move to an aftermarket exhaust system or freer-flowing air box.