2012 Merc 115-4S dropping rpm SB 522CR

[bacaruda]

First time out this year. When running up full throttle, as just getting over 31mph, feels like throttle pulled back 25%. Did not see RPM. Then it picks back up, then drops again. No alarm. 3/4 tank fuel. Temp gauge not working, but no alarm. 125hrs on motor. Cruised 20mph@4500 for over an hour no problem. Good tell-tale. Water pump? Why no alarm if hot? Does this have a rev limiter? It does not feel like miss, just loss of RPM.

Jim

[Bryden24shp]

It doesn't sound like an overheat problem, easy way to tell... Is the water pump pissing a good stream? If it is, is probably fine. Fresh fuel? Has the fuel filter and water separator been changed? Could be a collapsing fuel line, or if they are not ethanol compliant, and you are burning ethanol, they can separate internally. Its really hard to say, but it sounds like its fuel related to me. Good luck with her, Jim! Let us know what you find out...

[Bamaman]

I agree with Bryan--fuel delivery issue possibly. Start by replacing the spin on water separator/filter, fi equipped with one. And check to see if there's a secondary internal fuel filter going to the fuel injection system.

[rancherlee]

Sounds like how my Suzuki acts if I have a plug going bad, though mine seems really sensitive to plugs. Lucky for me a set of plugs is a 5 minute job and I just change them every year now in the spring before my first outing. I've also had EFI 4 strokes act up like that if water has built up in the high pressure fuel pump chamber.

[bacaruda]

Thanks guys things to check. It doesn't have a fuel/water seperator filter. 1 low pressure filter and 2 high pressure. All like inline filters. But I think it has a big filter/seperator installed in the battery compartment. Dealer item that I would have done. 2012 vintage so definitely ehanol tolerant.
Just a thought, I mentioned not checking tach. I believe I have been running 30@6300. If I hit 31 or higher which I did, it would have hit the 6500 rev limiter. Hope that's it, now I H A V E to buy that new Merc SpifireX7 prop I've been drooling/waiting for! Can't test or anything again 'till Wed.
Oh yeah, fresh fuel 3/4 tank in the fall W Sta-Bil. Always land gas, not from marina.

Thks.,

Jim.

[ron nh]

Check out Boat cops recent thread about the 115. Don't know if that's your issue but he posted a link to mercury's service bulletin. Fuel supply module problem from 2005 till present.

[slingshot]

I think the tell tail is that "this is your first time out this year". Did you have the motor and fuel system winterized? how long has the fuel been sitting in your tank? If you plan on leaving fuel in your tank for a long period of time always fill it to the top and use Sta-bil as you did. Possible water in your tank. If you don't have a water/fuel separator, get one. Change plugs, Change any fuel filters. Make sure your fuel is fresh. Change that oil. Good luck.

[teecro]

I think the tell tail is that "this is your first time out this year". Did you have the motor and fuel system winterized? how long has the fuel been sitting in your tank? If you plan on leaving fuel in your tank for a long period of time always fill it to the top and use Sta-bil as you did. Possible water in your tank. If you don't have a water/fuel separator, get one. Change plugs, Change any fuel filters. Make sure your fuel is fresh. Change that oil. Good luck.

Sta-Bil is cheap insurance... I add it to every fill up every time....

[haganjeff]

My guess is you are hitting the rev limiter. Mine does that at WOT and I trim too high, it immediately loses rpm..my two cents!

[bacaruda]

long overdue update. A few days after last post took boat out. Could NOT duplicate symptom. Ran up to bumping 31, not solid, and same with RPM. Could not get 6500 to test limiter theory. Just shy maybe 6450. Ran like a top.
Now have new Spitfire X7 prop, got rpm down 5800-5900, just touched 33mph new high. Again ran flawless during 20min test.
Now last weekend, running up to 28mph, 5500rpm did it again. Drop rpm, turn off, whatever, then pick up. Too cool air to do alot of running around with wife. So much for rev limiter theory.
Went down today to check inline filter/water seperator. Big unit, Yamaha cartridge. Did not find a drop of water.

New ideas?

[bacaruda]

Oh BTW looking at some related threads yesterday. With todays 10% ethanol gas, that should take care of any unoccupied fuel tank space condensation, As the ethanol can be a gas drier.

Jim.

[PlaynDoc]

It kinda sounds like the problem i was having... RPM's great one moment, crappy the next; unpredictable....

Here is the topic: viewtopic.php?f=2&t=22369&hilit=singleton+marine

here is a cut and paste from the posting...

"Their report said: Found float is stuck on full.

So, they removed and replaced float switch, seal, and hose, along with remove and replace damaged oil filter.

All under warranty. My cost: $0.00, other than towing it 1.5 hours each way, to get it to the right place, for the right repair.

When I picked it up, I took it out on the lake, and ran the hell out of it for about 2 hours. Ran great.

I have no idea what the cost would have been, but here are the part numbers:

26-880596502 Seal
8M6000359 Float
32-880596A05 Hose Kit
8M0082911 Air Filter"

[bacaruda]

Thanks playdoc, not same symptoms. It runs fine up to max rpm. Then like you shut off for 1/2sec then on. Then picks back up. Like last post too cool to test a lot with wifie on board.

Thanks,,

[bacaruda]

Update, ran about 18-20 gal through it yesterday at WOT pulling BigMable, not a hitch, ran flawless.