2011 Yamaha 4 stroke 25hp motor stalls or won't restart after running

[Evil Wake]

I just purchased an electric start 2011 Yamaha 4 stroke, 25 hp on a 17' pontoon boat. The motor has only 20 hours on it. The motor starts great and runs so quiet and smooth but sometimes stalls and will not start. We took it out only 3 times after purchase. 1st time stalled after 15 min running and would not restart (paddled it home). 2nd time ran for 30 min. then we turned it off for 10 min and it would not restart (paddled it home). Five hours later started no problem. Next morning started no problem so we dropped it at the local marina for repair (they haven't found anything so far). Oil looks clean and sufficient. Dealer (consignment) says he put premium gas in it but the marina says the gas in the filter looked a little old and there was a small amount of water in the filter. Any ideas/suggestions? Kayaks are meant for paddling....not pontoon boats.

 

[99yam40]

need to find out if it is getting spark when it will not start

 

[tomhath]

Sounds like it's overheating a little, either from running lean, not enough cooling water, or both. .

Dump all the old gas and refill with premium that has stabilizer in it. Adjust the mixture to be a tad on the rich side.

Make sure you have a good flow of cooling water, maybe replace the impeller anyway just to be sure. It's not difficult or expensive if you do it yourself.

After you make a high speed run with it, shift into neutral and let it cool down at slightly above idle for a few minutes (not just 30 seconds, a few minutes). If you shut it off too soon all the cooling water drains out and the power head overheats.

 

[pro-crastinator]

Above post is good advice.
I'm leaning towards it sounding like it could be a fuel problem.
Carb is probably fouled but I wouldnt tear into it until I tried some fresh gas, ethanol free and a new set of plugs.
Think about pulling the carb bowl and see what it looks like.
Consider the Yamalube additives. Fuel treatment and the ring free stuff.
The extra additive crap really is not that costly when you look at the big picture.

Afterthought: I recall the dealer telling me that lack of use of my new outboard can generate a negative outcome on performance.
He told me to run her every 2 weeks. 2015 Yamaha F25
good advice / bad advice - too soon to tell.