Ok was in a poker run this weekend when running about 4000 rpms all was ok. Slowed down and bam Port motor just shut off. Tried to restart but just smoke out of the exhaust and intake? Let it sit for a while then tried to start it and it ran but real bad with a miss. Shut it down and loaded it up on trailer. Got home pulled the plugs and Number one spark plug looked like someone hit the tip with a hammer. Checked for compresion and there is 0 Any ideas? Just a valve? Worse?

Sounds like a valve broke and bounced around in there. Pull the valve cover.

in a word "detonation. "

Plan on taking motor apart. Will find either valve parts missing, part of the piston missing, and or both.

Could be from getting hot, bad gass, too much timming, 2 lean at that throttle setting, bad fuel pump, & ???

Never got hot and is a twin engine boat. Got fuel the night before at the marina?

if you slowed down real fast water might have backwashed in the exhaust, pull the head and take a look, cold water can make the valve seat drop

That is what someone else said. It is at the race shop so I hope to find out soon. Thanks for the help