This sounds almost exactly like what happened to mine, we rode for about a half hour stopped, 2 hours later the thing would barely start much less run at all, I knew there had to be some sort of unknown damage going on well prior to that. Obviously something finally gave up though. I filled both cars with it last night as I'm draining the tank again, I'll be mixing new with race gas when it's done. We filled up with around 45 gallons prior to this trip so I couldn't help but see that as being the root of the problem. I'll post some pics of the plugs when I get a chance, I didn't take any while I was doing the compression test other than the smashed one.

And I said check the marina. Have one here that sold 110 and messed up and had it switched too 91. Blew up guys engines and he was told too pound salt too. I also don't believe half of them with no ethanol. Here's my deal I bought a brand new ranger and filled from the same marina for 3 years. Went out a month later and boat died. Two gummed up fuel pumps and all new fuel lines plus clean injectors later all from ethanol. This marina has a big 10 foot by 3 foot sign "no ethanol" ..... lost my biz forever and gave too mechanic down here too show what lies and decite they are capable of.

Which marina on which lakes guys?

Cole I can't really say cause I do all their fiberglass work. But ask any high performance boater on gRand and they will tell you. I buy all my gas now from serenity point. Their 91 came back at 93 this summer. ConocoPhillips tested it for me through a friend. Not one drop of ethanol. Just sayin.

Ok, I run a simular setup, if it ran decent for a while, where was the timing set at ? I run AC R42TS for over 3 years now, timing @ 28, you can get one the small camera's and look thru the plug holes to see that things look like, but going to have to come apart I'm thinking...again pics of plugs would help...Rob

You have to pull the heads and see whats up. No biggie, without air tools have them off in less than an hour. Never mind bore scope, plug reading. You know ZERO compression in one of the holes. Pull them and post pix after you tweek out and dummy a few beers.Bet tops of pistons look like the surface of the moon and valve heads if still there coated with rough grainy aluminum sand. Feel your pain Bro...

That's my thoughts about it too but in not even pulling the heads right away, taking the whole thing out because I'm 110% sure the pistons are gone at the very least. Hoping with stock cast heads that they've faired a little better, will know once it's out.

Dont rule out your intercooler,,it might have a hole in it and injecting water into the carb..you said hard starting which the engine could have been trying to start on water with the fuel.. pressure test the cooler..

That thought crossed my mind last night too as I was starting to get it ready to come out, as well as testing the headers. Cooler was tested before it was used but definitely worth a second look.

Well guys I've got an update....
Pulled the engine Friday and tore it down this afternoon and found out the exhaust valve seat on #4 cylinder was gone, and pieces of it had visited all the other cylinders. The pistons looked like someone took a punch and a hammer and beat the tops, #4 being the worst by far and the heads were pretty well matching. The cylinder walls have some marks but nothing horrible, but I suspect the heads are beyond repair and one of them was new with the build as the original was cracked. The valves are about 50/50 as far as being salvageable. The other cylinders look like they've been running rich and burning properly as they should have been. Not sure what would have cause it to come out but one thing I did notice was with a thermostatic oil cooler and no thermostat the engine temp would take some pretty heavy temp swings. Guess I'll be making some calls tomorrow and see where to go from here, get things going so we can have her going again by boating season!