sludge in my 15 hp Johnson

[Ilikesalmon]

I have a 1987 15 hp Johnson that seems to be running rich. The owners manual says to mix the gas and oil at 100 to 1, however, they have since changed this to 50 to 1 and that is what I do. After trolling , there is a considerable amount of sludge coming out the exhaust port. Can I fix this? Or should I leave it alone? The motor runs so well now, that I am hesitant to do anything to it without some expert suggestions. Any advise would help me.

 

[BF]

Re: sludge in my 15 hp Johnson

Hiya & welcome!<br /><br />50:1 is correct. You might try turning the low speed mixture adjustment towards lean a bit (move 1/8 to 1/16 of a turn and then wait to see that it still runs smooth). If it's running great then there isn't really much to fix, but if it fouls plugs after lots of trolling, you might consider switching to different plugs (perhaps to NGK's... I forget what the correct number would be for that one).<br /><br />Maybe consider de-carb'ing the motor (do a search for "seafoam" or "deep creep" here). I decarb'd my 15 hp for the first time 2 weeks ago.. I was impressed at how much smoother it was afterwards (and I thought it was good before). <br /><br />Other's seem to swear by synthetic oils (or synthetic blends), maybe they'd also decrease the "sludge factor" a bit. (?) I haven't had any direct experience with 'em.<br /><br />I posted this link for someone else below, but you'll like it too.<br /> 15 hp maintenance article <br /><br />good luck,<br /><br />Brent

 

[knobby]

Re: sludge in my 15 hp Johnson

2 tanks, 100:1 for trolling, 50:1 for getting there and back.

 

[Ilikesalmon]

Re: sludge in my 15 hp Johnson

Hey Bf, I did the de-carb about two weeks ago and it didn't seem to help much with the sludge but it did make the motor run better! I have the recommended Champion plugs in it now, (but I can't remember the numbers.) I hadn't thought of using synthetic oil though. I will give it a try. When I am trolling, I turn the rich/lean knob as far to the "lean setting" as possible and it still forms the sludge. Maybe a "carb kit" would help since it has been maybe four years since that was done. I know these two cycle motors are "dirty" even when they are running good, but I still would like to reduce the pollution as much as I can. Thanks for the advise!

 

[BF]

Re: sludge in my 15 hp Johnson

Hi again, <br /><br />Even if the outer knob is all the way to "lean", anybody could've pulled the knob off and re-installed it a different way. I'd pull the knob, and lean it out at idle until you can tell it's a bit too lean, and then richen it back to the "sweet spot". Put the knob on so the "sweet spot" is when the indicator is in the middle of the range.<br /><br />If you recently de-carbed and haven't run the engine fast very much (always at idle), maybe it's still sludge coming out from that (?).<br /><br />Have you checked your lower unit oil lately? The reason I ask is that on another of my motors (which seemed a bit sludgy, but is new to me so I didn't know what "normal" was), I found that there was a small leak in the lower unit near water pickup. I think a bit of gear oil/water mixture was being sucked into the water pump. Made funny looking exhaust residue, and also had a bit of water in LU.<br /><br />good luck.<br /><br />Brent