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The Issue:

I recently purchased a 9 kilowatt generator running on a 17hp Briggs and Stratton engine which ran pretty well when I first bought it except for a little white smoke.

I replaced the gasoline just to be safe as the owner had not run the generator for several years. The generator ran great after changing the gasoline. I don't remember seeing any white smoke either.

Then I replaced the oil and put cleaner in the carburetor (or what I thought was the carburetor). What I actually shot with carburetor cleaner was the fuel pump! After this, the generator would only turn on for at most 20 seconds then a ton of white smoke would shoot out and the generator would quickly die after that. Come to find out that a bunch of gas was spilling over into the oil section and I assume oil was also feeding back into the cylinder.

I then replaced the fuel pump, carburetor float and needle valve. I also replaced the gasoline-filled oil. Now the generator runs beautiful, except that now there is a steadily increasing amount of white smoke coming from the exhaust. It takes about 10 seconds for any white smoke to be visible and steadily more and more white smoke is visible until it looks like a fog machine by about 90 seconds. Once I turn off the engine, white smoke continues to steam from the exhaust for about another two minutes, steadily decreasing.

The Question:

There is no oil that I can see around the crankshaft or the gasket. The oil level is staying at the exact spot and is not too full. From what it smells like, I believe that oil is burning, but I do not have the experience to tell where it could be coming from. Anyone have any ideas of what could be causing the smoke?

  • Are you sure it's smoke, and not steam? Is it possible that there could be water down in the exhaust pipe? Is it an exhaust stack with the opening toward the sky, or is the opening out the side? – Tester101 Jul 17 '15 at 12:02
  • Hey @Tester101. Thanks for your reply. The exhaust is pointing out the side. It is not water or gasoline. Holding your hand over the exhaust, through the smoke will leave little droplets that never dry... Definite sign of oil. – KJ Price Jul 17 '15 at 12:51
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    I second that--white smoke is burning oil. – Craig Jul 18 '15 at 6:44
  • Might just get by with a heavier oil for a worn or high mileage engine. – Iggy Sep 21 '17 at 13:06
  • Is the choke stuck this can cause excessive smoking because the fuel air ratio is off. I would suggest rings or valve guides but you said it was not burning any oil. – Ed Beal Sep 22 '17 at 16:06
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My guesses without more information would include the crankcase being overfilled with oil, a blown head gasket, or damage to the piston, rings or cylinders.

I doubt that you have the generator running while it sits at an angle, which could let oil slop over into the carburetor float bowl. Although that's a possibility, too, if you have it sitting on a slope.

Since the engine apparently always produced a little while smoke, and since the smoke doesn't start for a while, then doesn't stop for a while after shutting the engine off, it's probably heat-related in one way or another. As the engine heats up, it expands. If there's a damaged head gasket or something like a hairline crack in a cylinder wall, it could open up just enough to let oil seep through once the engine is hot. Or if you have something like damaged or ill-fitting piston rings, oil might start squeezing past the rings once the engine heats up and the cylinder expands.

You mentioned that if you hold your hand in the white exhaust, little oil droplets condense on your hand. The same thing is happening inside the exhaust manifold/pipe, and the heat will cause that condensate to keep smoking until it is all burned off or the temperature drops low enough for it to stop smoking. If the exhaust valve is open at all after the engine shuts off, any oil in the cylinder will burn off and push white smoke out the exhaust, as well. Especially if it's some kind of hairline crack letting oil into the cylinder, which then closes back up as the engine cools.

Of those possibilities, aside from overfill or running the engine on a slope, the head gasket would be the easiest thing for you to fix yourself. You would need a torque wrench and specifications on the correct bolt tightening pattern and torque for the head bolts for your specific engine.

Or it could be something completely different.

Here's a potentially handy page from Briggs and Stratton, but it might be time to call a local small engine repair shop.

https://www.briggsandstratton.com/us/en/support/faqs/engine-emits-white-blue-smoke

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From another website I have a Cub Cadet LT1018 with a Briggs 31Q777-0305E1. I ran across this thread while researching my problem, so I thought I would share my experience (and my stupidity) for others to learn. My fuel pump was leaking gas last summer, so I replaced it with the Briggs part. It started leaking gas again this fall, so this time I used an aftermarket part from Oregon. I installed the pump, and the engine started up just fine but then I started noticing white smoke. I shut the engine off and got a huge backfire (repeated this 2 more times and it backfired each time). I then parked it and let it run for 10 minutes but the white smoke started getting bad. I turned on the blades and a huge puff of white smoke came out. Then the motor died and wouldn't restart. I checked the oil and it was low. I then took off the carb and the carb was full of oil. I drained the oil and the oil smelled like gas. Based on the info from this web site, I assumed I had a blown head gasket, so I removed the head. I did have a blown head gasket, so I replaced it but the engine still wouldn't start. At first I assumed the carb was jacked up from all of the oil but then I decided to inject gas into the carb bowl...surprise, the engine ran for 10 seconds. Next step, pull the fuel line that runs from the pump to the carb and see if fuel is pumping...it was not. Fast forward a few days of thinking and I realized that I accidentally reversed the pulse and fuel input lines when replacing the pump. I was sucking oil from the crank and sending it straight into the carb. I switched the lines and everything works great now. Well, I also change the oil twice and the oil filter once.

The only thing I couldn't figure out was: How was the engine even running with these lines reversed? All I can figure is this. Right before the fuel pump change, I topped off the gas tank to the very very top. I think that the gas was just running to the carb due to gravity. Once the tank got a little lower, the motor stopped because it had no gas. It had no gas because gravity could no longer feed the carb. In a way, this was a good thing because if the engine had kept running, I would have burned all oil and blown the motor.

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