Gravity fed fuel system or fuel pump on the mower?
If it has a gravity fed system, and there is no manual, inline fuel cutoff valve (or the valve is not being turned off when the mower is stored) the carb might be leaking some fuel into the crankcase. After 5 minutes or so of running, the fuel will begin to boil off and pressurize the crankcase. The pressure will vent out of the crankcase through the breather, carrying oil mist with it. This mixture then gets burned in the combustion chamber to the tune of a lot of smoke.
Has it done this every time you try to run it lately, or just one time?

IF shutting the gas off when engine isn't running doesn't clear up the problem, think head gasket.

Walt Conner

You should be checking the oil before starting the engine anyway and gas contamination of oil is going to show over full.

Walt Conner

Ditto what Walt said about ALWAYS checking the oil before you start the engine. If the oil appears even a little bit higher than it should be, and you know it was not that high before......you might be seeing evidence of a leaking carb if it has a gravity fed fuel system. It does not take much gas in the oil to cause the boil off issue to occur.

It's doing each time she tries to use it and also for me when I took a look at it. I wasn't sure of oil contamination with gas so I changed it and it still smoked shortly (5 or so minutes) after start up.

She does check oil before use, but its hard for me to keep tabs on just how much oil she is adding, but it was at normal level when I checked it.

I admit I didn't pay to much attention as if it is gravity fed or runs a fuel pump. Guessing I would say gravity fed and I did not notice a fuel leak around the carb. It does have an electrical connection on the carb bowl if I remember right that I don't understand what it controls? I live 60 miles away and my memory isn't what it use to be.

It will be a few days before I get back up there and I might bring it back to my place to work on it.

Based on this info, if it supports any other ideas let me know please.

Thanks.

Even if it has a fuel pump, IF the gas tank outlet is above the carb inlet, it can leak gas thru the carb. You will not see anything outside courtesy of your friendly EPA. They figure it is better to ruin your engine than leak a few drops of gasoline on ground.

That solenoid on the bottom of the carb shuts the gas off to the main metering jet to help prevent "after fire", does not shut gas off from leaking thru carb. The solenoid MUST have 12 V to it to open it to run. You should hear it click when the ignition switch is turned on.

Walt Conner

I brought the mower home but before putting it on the trailer I checked the oil level and it hasn't increased in the past couple of weeks its benn sitting with the fuel on. I did notice an accumulation of an oily residue in the base of the air filter housing.

Since it doesn't appear that fuel is migrating into the crankcase, should I start with the head gasket? Something else first?

It did smoke very slightly at start up but not a concern. Didn't run it long enough to see if it was going to make a smoke cover though.

Thanks.

" I did notice an accumulation of an oily residue in the base of the air filter housing. "

Your symptoms AND what you said above is a fair indication that the head gasket is blown. They always blow between the cylinder and push rod gallery so this pressurizes the crankcase blowing oil into air cleaner box and sucking oil into cylinder. Head gasket about $7.

I have detailed instructions on valve adjustment which will include head bolt torque and pattern. You can probably download a free Service Manual at http://www.mymowerparts.com/pdf/

Even then, my instructions have some pointers not included in the Service Manual. IF you want them, Address below, put in proper format and remind me what you need.

Walt Conner
wconner5 at verizon dot net

Thanks Walt, I may have the info but if I don't I know who to ask!

Walt, It looks like you were on the money with the head gasket. Only evidence of problem was where you mentioned. I replaced it this afternoon and ran it for 20 plus minutes with no problems, which was more than long enough to get it smoking before. Thanks.

One other issue that I might want to address is a extension that was put on to help drain the oil. It is a pipe threaded peice that appears to be seeping a small amount of oil. I snugged it up a liitle but still has a few drips. Do I dare wrap some teflon tape around the threads? Right now I'm a little worried about the intregity of the threads. It's where the drain plug would normally thread into the case.

"Do I dare wrap some teflon tape around the threads?"

No problem, you may want to wait until time to change OR tilt the mower over 45 degrees or so to clear oil drain hole.

Walt Conner

Thanks to all that responded to my questions. I decided to wait to the fall oil change to address the oil drain problem.

I'm a newcomer to houzz, but appreciated greatly factorypilot and walt's discussion. I'm also a beginning novice at small engine repalr. I have the same size engine, but it's a 287707 0225 01 single. It would start for ten seconds, then blue smoke, sputter and die. I cleaned the spark plug, waited a few minutes, and it would repeat the same thing. Opened the air cleaner compartment, and bottom of filter screen (foam) was wet with oil and gas mixture. I cleaned the plug again, leaving the filter and filter cover off. It started, but then began spurting oil/gas mix out of the crankcase breather portal. The gas is gravity feed to the carb , with no manual shut-off. The electrical connection at the bottom has the following designation on it. - 76-511 4294. No leaking from the carb area, and to my knowledge hasn't been touched for 25 years. I bought mower used in '96 and it was probably 5-10 years old then. I pulled the valve cover off - a little oil residue in there, and then the head. Gasket seemed in perfect condition - no deterioriation or breaks. I tried to pull the filter housing bottom off, but the one screw didn't allow it to separate from the intake manifold or carb body. Not sure how that comes off - and spindle for valve cover nuts doesn't appear to have anywhere to attach a wrench to pull it out. I'm not a carb person, so not sure what I'd do if I was able to open it up. Suggestions would be greatly appreciated.