Random No Start-Bad Compression on 50 HP 2 Stroke?

I have a 2000 50 Hp 2 stroke that I bought new. I had random starting problems with the motor recently and I had it towed into the marina 2-3 times. It would run fine I would take it back out and then just randomly not start. There was water in the gas from a gas cap not sealing properly at one point last year. We drained the tank and reinstalled. The marina is saying there is unbalanced compression in the cylinders 110-90-80 now and they are 80% sure that the problem is bad compression. They are saying in 2000 Mercury used a foam core head and it cannot be repaired, only replaced? Does this make sense? Are there any other procedures to check or other options before I make a decision? Spending $3500 on buying a head and repairing a motor on a pontoon that is only worth $4-$5000 seems crazy.

Re: Random No Start-Bad Compression on 50 HP 2 Stroke?

Don't go back to that dealer except to order parts, and even then, check prices elsewhere to compare.

Merc does NOT use a cyl head on most of their engines, instead the head is part of the block casting. Piston installation is through the crankcase half.

You should do the compression test again, yourself, to verify that all cyls read different. Only then can you be sure what is going on.

If indeed they are that different, then remove the exhaust side cover so you can inspect the cyls and pistons to see if they are scored and in need of boring the cyls and installing new pistons. It is possible that the ring lands on the pistons are 'gummed up' causing the rings to 'stick', reducing compression. If so, you can replace the exhaust cover (with new gaskets) and begin 'decarb'ing' the motor to remove the gummy deposits and restore some compression.