I got a 2005 4mill 421 cub, 35 pwk carbs, V force 4 reeds, Toomey's. I built it in January and had took to have dyno'ed. I've taken it to the dunes and rode it around my house and it ran good, then I took it to the dunes last weekend and fouled probably 8 plugs in 2 days and it was mostly on the left side. What can be causing it to keep fouling plugs like that?