my six pak is brand new...i need to replace the power valve as i had a slight misfire thru the center carb...why plugs???? my personal experience is that champion plugs suck...I had the same issue as this fella... ran lousy at idle and was popping thru the exhaust...i changed my plugs to ac...and the car stopped popping and ran well even with the power valve issue...as I said it worked for ME...