sled runs good but it will foul the plug on the clutch side, other side is perfect brown on the tip and the clutch side is black. i switch them and it runs on 2 again. black plug will turn brown and brown one will run good for awile then foul. both carbs are set the same i have no idea what this could be. i run ngk br8es in it because those were the plugs in the engine when i got it.