Briggs & Stratton emitting white smoke.

Broken piston ring(s) is a good bet.

If this is one of the `flymo` type mowers do you by any chance store it in the garage by hanging it by the handle? I have on numerous occasions to clean out engines that have been treated this way.Usually only removing the plug and adding a drop of petrol into the cylinder does the trick.

Yep - my money is on those rings....good luck!

Over filled with oil? Some one put fuel mixed for two stroke engine in a four stroke? Bad valve guides?

I don't think its overfilled with oil, as it ran ok for 34 of the 36 months I've owned it; & I've never had to add oil. I'm the only one that has used it, and I've never put 2-stroke fuel in it. I estimate the total actual hours of operation at 3 hours in 3 years since new. Would that cause enough wear to affect the guides to that degree?

Shouldn't, I've had Briggs and Stratton engines last for 15, 16 and 20 years with out as much as an oil change. This is with weekly use in Alabama where you can find yourself mowing the lawn on New Years day if you plane fescue. (That is why I now have bermuda grass)

It shouldn't cause wear, but oil can turn to gum, not lubricate properly, and lead to stuck rings which are just as bad as cracked / broken rings. Try draining off some oil and add in some Marvel Mystery Oil. The engine will doubtless smoke even more for awhile, but if run long enough will free the rings. If the smoking persists, the rings are smoked and very likely the cylinder bore as well.

Good morning ozzb. You and others were correct in suspecting fuel contamination and overfilled oil. The repair shop said there was water in the fuel, AND oil. I suspect what he was actually seeing was mogas that had gone bad. Since the engine is only run less than a minute, about 160 times a year, I figure the mogas went bad after 3 years. From now on, I'm only using avgas in it.

I'm still trying to figure out how the fuel got into the oil tho.

Had a similar prob with a B&S, left fuel in the tank and stored it over winter, leaky needle and seat/diaphragm (cant remember 30 years ago) caused fuel to drip into the combustion chamber(inlet valve was unluckily open) seeped thru the piston rings into the crankcase, the rest was a run big end and a frightfull death. Never left fuel in a tank again for storage.

Bluish white smoke from an engine exhaust is usually oil gettiing in and not burning during the exhaust exhaust cycle. Oil on the spark plug is a good indication of this.

Dark smoke from oil leakage would be from oil leaking in during intake and being burned. Or from excess fuel due to a clogged filter or partly closed choke that would cause power loss and rough running and a soon empty tank.

The gas and oil should be replaced each year because gas "goes bad" and oil absorbs moisture. Rarely using the mower for a long period and leaving fuel and oil unchanged is not a good idea.

Old gas gets gummy and could "glue" engine components (rings) that have been in contact with it for a long time. Use a gas stabilizer like STA-BIL with new gas if you really don't want to empty out your fuel system during a long storage period. Stabilizers don't work with old gas that is already effected.

Your piston made need a "Gumout" treatment to free the rings.

http://yardener.com/LawnMowerMaintenance.html

Jon

As to the symptoms if poor engine breathing described--

Those are the more likely explanations...except one thing was left out...something not mentioned that should have been checked early on: the condition and sealing of the breather. A stuck (non-breathing) breather can cause excess oil to be drawn into the chamber...with resulting oil fouling of plugs and blackening of chamber...sometimes oil will be drawn across into the carb through the crossover pipe as well. You'd be well-advised to change the breather element and seal gasket as a matter of routine maintenance regardless of its apparent condition: the cost is so little, and the likelihood of fault elimination so good that there's no reason to fret over cost. You'd be surprised just how many B&S engines are retired prematurely only for lack of renewing (or even knowing about) the breather. Additionally, machines that sit long periods in inclement weather conditions are quite prone to breather valve hardening and subsequent malfunction.

Would also recommend head removal and scraping to the piston and chamber...as the reduced capacity caused by carbon deposits (from the too-rich/low-aspirated burning) will cause overcompression stresses and heating during engine operation.

Good morning guest. Thx for the headsup. I assume by 'breather', you are referring to the air cleaner filter element. I am not familiar with the 'crossover' pipe. I imagine the local auto parts stores, like Checker & Napa, are good sources for filters, gaskets, etc.

Good morning Jon, thx for the tips and the link. I will do better maintenance from now on.

Someone mixed antifreeze in with the fuel?

Good morning bwire. The antifreeze theory is almost impossible, as the engine is stored in a locked area when not in use.

Do you use ti to cut along any steep slopes? My lawn mower will burn oil when I cut my slope while pushing it in one direction but it doesn't when pushing it in the other direction.

Good morning scotchdrnkr. Nope, the unit is always used on level ground.

You clearly have incomplete combustion and that should be addressed first before worrying about the color of the exhaust smoke. Change the spark plug and the ignition points (if this engine is equipped with points); make certain the air filter is clean and the choke is off when the engine is running. Change the oil and refill the crankcase with synthetic oil which has much stronger detergent properties than regular mineral oil and will remove the soot that has built up in the engine. I suspect that will solve the smoke problem. If not refill with fresh gasoline: perhaps the smoke was caused by too much anti-gum additive in the gasoline.

White smoke from internal combusion engines is usually caused by burning coolant but the B&S is air cooled.

Dennis Waller

"My 3-year old 6 hp Briggs & Stratton lawn mower engine started emitting white smoke last winter"

Maybe you should wait for the snow to melt?

Sorry, couldnt resist

Last year mine did that and I had gasoline in the oil. When I took the carb apart, it was all stopped up with a black tar like rubber that appears to have come from the gasoline disolving the rubber gasline. This made the float stick open and it drined into the combustion chamber. The only place I got gas for the mower was at a local Shell station. I now do not buy Shell gasoline. I think they have been monkeying around with addatives that were not compatable with the mower gaslines. So I replaced the gaslines and cleaned the carborator and everything worked fine until I go gas tat Shell again. I then drained the gas into a glass jar and let it sit. There were some stuff the settled to the bottom. I don't know what it is but it's not gasoline. I then added a little antifreeze to it (I ggogled the problem). It showed that there was about 10% alcohol and 5% water in the mixture. I repeat, I don't buy Shell gasoline anymore.

I have seen this problem on various overhead valve small engines. I have found that the most common problems are the head gasket on overhead valve engines can break between the valve train and the combustion chamber causing oil to be drawn into the cylinder or the compression to leak out into the case and push oil out of the case breather into the intake and sucked into the cylinder that way. The case breather can be located by following the small rubber tube that connects from the intake manifold to the engine block there is usually a metal plate with two screws, the filter should be under that. it couldn't hurt to have a look at the filter / clean or replace it. You could also look into the carb throat to see if there is any oil on the air filter or in the intake. Smoke from burning oil usualy has a blue tint where smoke from unburned fuel usualy has a black tint

I had problems with a Snapper mower with a B&S that was "making oil" and smoking. It turned out to be a faulty needle/seat in the carburator float valve.

The fuel was leaking through the carb into the intake and seeping past the intake valve and piston rings. I checked on a new carb, but chickened out when I found out what they cost. It was just too much to spend on so old a mower.

I used it until the deck rusted out by simply remembering to turn off the fuel at the tank tap every time I used it and then running the carburator dry before putting it away.

I do the same thing to my generator I keep for power outages. Turn off the fuel at the tank and run the carb dry. It keeps deposits from building up in the float bowl and makes certain that the fuel in the float bowl is as new as what is in the tank when starting the thing up.

I have seen the crank case breather get stopped up and cause oil leaks and oil burning when the oil is not changed regularly. It happens rarely but is pretty easy to clean with some Gumout after you finally get the thing out where you can get to it to clean it. I have also used the old carburator soak, GUNK Hydroseal, on them but it always takes the paint off and I haven't seen that stuff in years. This problem used to be a lot more common back when people used non detergent oil in these motors. The breather would eventually stop up even if the oil were kept changed on schedule.

Have FUN!
TT3