First of all NightHawk never said anything about it not doing it in neutral. He did clearly say it was backfiring through the exhaust,not the flame arrestor and only above 4K rpm's.

Your problem could be anything. Someone that revs and holds their engine steady over 5K rpm's in neutral is just asking for problems! You can't even tell if a engine is missing on a cylinder at 5K rpm's in neutral. Your mechanic must love you.

Thanks for all the suggestions.

It's difficult to imagine a spark plug at fault if indeed the backfire is through the exahust. The engine had no fault codes on the scan tool other than the usual ones. I'm guessing a lean condition would also cause a backfire from the intake and not the exahust.

So I think the most important thing he needs to do is get the boat back in the water and verify with certainity it's coming from the exahust and which side. I'll probably need to follow him to see if it's coming from one side or the other.

I am my mechanic. I know old school carburetor and nitrous drag racing though. Just looking for advice from boat pros here. Appreciate any info, thanks.

Did you get back out to see what's going on?

The boat's owner can't get back out until Saturday. I plan to follow him closely in my boat and watch the exahust.

I got mine out today with some new plugs and it ran perfect. Used the $4.00 Autolites. Old plugs really didn't look that bad and had 228 hours. Thanks for the input guys. Hopefully that's all it is for Nighthawk's buddy. Good luck.

Do you have a newer 496/8.1 engine???

2001 496 Ho.

My friend put a fresh set of plugs in before he put the boat back in the water Saturday. Problem solved. It must have been coming from the intake.

:drink: :coolcowboy: Good to here that it was not a big problem, what did the old plugs look like??? thank's