Pontoon Boat & Deck Boat Forum

Had boat out first time this year. A little sluggish at first but picked up and ran fine most of the afternoon. We were cruising about 20mph or so, and saw fellow tooner, pulled up to chat while engine idling. While idling for 5-10 min., I noticed a little miss. Went to take off and sputtered and died. Started multiple times but would not go. Finally wouldn't start. Got a tow back to dock and pulled cover. Found I had left oil filler cap off from oil change. Could crankcase venting oil vapor inside cowling cause plug fowling? Also noticed air filter element gone. Looks like had broken-up probably ingested. Now the filter issue could have been anytime, as is this a 2012 boat.
Anyway, with cowl off and oil cap on, it now started fine and ran fast idle fine. Again could oil atmosphere cause this?
Going to get fresh sat of Denso plugs as nobody has the NGK's called for. Also might change low pressure filter.

Wife now paranoid, not going to watch fireworks tonight.

Jim.

I have to do plugs today, no one has ngk around here, need to do today for wensday after work trip.

Change plugs, check filter for water/ethanol crystals etc.

A 4stroke shouldn't foul plugs idling, 2 strokes can.

And if you had so much blowby that it could be injested and foul plugs....engine wouldnt run

Check gas for water or possible ethanol crystals in carbs....FI or carbs?

Thanks bansil,
I have to do plugs today, no one has ngk around here, need to do today for wensday after work trip.
I got Denso 5343 from Advance Auto, shows in cross reference, many, also was going to get Bosch 6713 if no Denso.

Change plugs, check filter for water/ethanol crystals etc.
Done, low press. filter good, could blow right through, no restriction I could tell.
No water, always land gas never had marina gas in decades. First I heard of ethanol crystals.
Sta-bil in fall.

A 4stroke shouldn't foul plugs idling, 2 strokes can.
Agreed, unless something amiss in combustion. Plugs were black, should have been near white, very light grey.
As mentioned, after removing cowl, fired right up like a breath of fresh air.

And if you had so much blowby that it could be injested and foul plugs....engine wouldnt run.
Don't realy mean to blame blowby, but oily mist atmosphere. Foam in top of cowl, fairly wet with oil. Also could see trace of oily film
on the water around lower unit. While doing maint., cleaned up top of power head and cowl pan where there was alot of oil film.
I've never whitnessed how much would come out of oil filler hole with engine at RPM and under load, don't have prop dyno.

Check gas for water or possible ethanol crystals in carbs....FI or carbs?
Really don't know how to check for water, or crystals never seen. Oh yes, 2012 engine. Didn't know they built 4S with carbs.
Even my 1991 175XRi is FI.

'Will know later today,
Thanks.

No idea on the carb vs FI

If you look in my build thread when i did my carbs you can see the orangish crystals...

Hope you get it running, i had to rebuild my fuel pump, the membrane was hard and cracked, after that it has been gtg...fuel pump diaphragm and gaskets was about $12...
I took it apart as diagnostic and sayed, thats bad

Sorry bansil, thought you had 115-4S too. I believe there were NO carb 4S at least Merc. Probably ALL early Honda's were carb for sure.
I haven't had a carb since my '80ish Chrysler 115.

Sorry to hear that. My 2012 Merc 115 4S has over 1,600 hours on it, and not a single hiccup.
No carb. It's EFI.