What type of spark plugs are you running ?
I was gonna ask the same question as to preferences. I happen to like ngk v grove plugs. what sold me on ngk plugs is when I put a champion in a dirt bike about 20 years ago and it fired and fouled right away, did not have that problem with ngk. my 66 chrysler 300 I had in high school would foul cyl 8 once in awhile with champions I then switched to ngk's and it would last alot longer. ngk plugs is what I prefer. some of the new dodge and jeeps are running ngk's now.