OK----this has been over 2 year project----replaced a 6.2 Merc w/ a 502/502 custom engine----everything brand new-did not use any parts / accessories from my blown engine----Have 9 hours on engine--all running like a top----went to start the other day---huge backfires out the exhaust--would not start----ran fine a few days before-------distributor was tight, had not moved--all wires tight---did some re-search and the minds told me it was my MaxVolt-mv-d6 ignition box-----(same as MSD) Talked to the company I purchased same from--they kinda agreed--installed a brand new one on today---SAME BACKFIRES???? Replaced my brand new MSD coil w/ another MSD coil----same---check inside the brand new distributor----all fine???????????? Any thoughts???? Mike--Tampa Bay !!!!!!