Why does my riding lawn mower blow white smoke when I go down hills?

Question

The oil level is not overfilled, and it sometimes doesn't smoke until I level out again. It doesn't smoke going up hill or on a flat, just down. It is a 7 year old Scott's 17HP mower that I got used from a person who rarely used it. It looks practically new! Any suggestions would be great!

Answer 1

I agree on the Carb. Going downhill there's less demand on the engine and if the mixture's too rich you're blowing some unburnt gas out the exhaust.

It still COULD be oil though getting by the rings or around the valve stems. If it's not losing any significant amount I'd just live with it.

Answer 2

The gas in the tank is running away from the intake hole in the bottom of the fuel tank when you go down hill. This allowes air to get into the fuel mixture resulting in a lean fuel/air ratio which results in the white smoke. About the only thing you can do to prevent this is keep the fuel tank full. Unless you are going downhill for long stretches, I wouldn't worry about the smoke. And don't worry about the carburetor, because if it runs fine on the level, the carb is not the problem.

Answer 3

Oil is passing thru the carb thu the plastic tube that comes off of the valve cover, going thru the engine and causing smoking.

Someone has inadvertently installed that cover plate on the valve cover 180degrees from its proper position. There is a baffle in there that needs to drain downward on the drain hole. Sometimes, also, that small drain hole in that baffle plugs and it will not drain.

So what happens is that engine sucks the oil right out of that baffle and thus smokes.

Answer 4

you are running against the compression and not burning the fuel as efficiently as when it is pulling. i wouldnt worry. oil smoke is not white.

Answer 5

get someone to check your carborator