Reducing Smoke in Exhaust from Two-stroke-power-cycle Outboard Engines

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
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Reducing Smoke in Exhaust from Two-stroke-power-cycle Outboard Engines

Postby DiamondDog » Tue Jan 09, 2018 7:08 pm

Is there a way to cut down on the smoke or redirect it somehow on a two-stroke-power-cycle outboard engine?

I'm not a fan of the noise or smoke at slow speeds. I was considering re-placing my 2008 90-HP Yamaha, but $10,000 is a non-starter for me right now.


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Re: Reducing Smoke

Postby pcrussell50 » Tue Jan 09, 2018 9:36 pm

If you're getting significant smoke while under way you may have a mechanical problem that will need fixing. Much above about five knots you should see nothing but a thin wisp of smoke, by which point you also won't be breathing it. When on plane you should see none at all and for sure not breathing it. Many two strokes make quite a cloud on first start from cold. That is normal and should dissipate. If it doesn't, you have a problem with your oil mixing system and will need to fix it.

Last edited by pcrussell50 on Thu Jan 11, 2018 12:43 am, edited 1 time in total.

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Re: Reducing Smoke

Postby dtmackey » Tue Jan 09, 2018 9:52 pm

DiamondDog wrote:Is there a way to cut down on the smoke or redirect it somehow on a 2-stroke?

On Yamaha motors there is a oil injection pump linkage with an adjustment that can sometimes wear or have been incorrectly set by the factory or after a dealer repair. Setting of this linkage is difficult - too little and the motor can run into too little oil, too much and is smokes, so most err on the too much side. There are claims that a full synthetic oil will smoke less and I have experienced this on my Yamaha 15 and 25hp motors after making the switch to full synthetic.


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Re: Reducing Smoke

Postby jimh » Wed Jan 10, 2018 7:33 am

In modern two-stroke-power-cycle engines the oil used is generally much improved over the older TCW3 oils. Using a better grade of oil will reduce smoke and also reduce carbon deposits. Try using Evinrude XD50 oil in older two-stroke-power-cycle engines.

The worst oil to use is usually the cheapest to buy: stuff like Walmart no-brand or Pennzoil. My old Mercury mechanic told me he could immediately tell engines he worked in which the owner had been running those brands of oil.

ASIDE: regarding exhaust emission from marine engines: here in the Great Lakes there are a number of artists who paint scenes of old freighters underway. Often the composition of the paintings may involve a meeting between two relatively famous old ships. There is one artist whose work is quite different than most: when he paints a scene depicting some famous old freighter from the 1950's, the ship is seen with a long plume of black smoke trailing behind it. I remember ships like that from my boyhood. I mostly saw them in the Detroit River, when they were running slowly. But when they were, literally, pouring the coal to their steam engines, they made black smoke.

In contrast, modern ships on the Great Lakes have flows from their stacks that are mostly white or gray--no more black smoke.