Small Engines (Lawn Mowers, etc.): lawn tractor smokin, rich fuel mixture, vacuum leak

Question
Eric,

Good morning and thank you for your reply.

The engine is a Briggs. The oil may need changing. It was last done late Spring in '03. It is dark
but doesn't smell burned. The dark smoke smells a little like rubber burning? It comes out for
about 1/2 second through the exhaust. The bluish smoke would suggest that it is oil. Is there a
filter? The only times this was done was when a Sears mechanic came to my house as part of the
maintenance program... usually once a year as I recall.

Can the carbuerator be adjusted for the fuel? I use unleaded gasoline from a Phillips 76
station...same as my Rodeo.

Thanks. Don

-------------------------
Followup To
Question -
Hey Eric - I have a 42 inch Sears 17 HP lawn tractor, 5 years old.
I kept the maintenace agreement active until last year and of
course now I have a problem. Maybe you can advise me as to the
possible cause(s)?

When I start the engine, a puff of dark smoke comes out of the
exhaust as-well-as when I turn the engine off, very strong smell.
When I shift into gear when running the same thing happens.
Now I can see a little smoke, bluish in color, puff out as I am
cutting. The oil level is where it needs to be, the filter is clean. I have
had to add about 8 oz of oil twice since this started about 3-4
months ago.

What are your ideas?  Thanks.

Don
Answer -
What engine it on the tractor? Tecumseh, Briggs, Kohler

Have you recently changed the oil.
The dark smoke indicates a rich fuel mixture and the bluish is oil, as you have probably figured
out.

Let me know about the oil change.  Oh yeah, does the oil smell like gas?
Eric

Answer
Some of the Briggs have oil filters, just look around the engine...it is just like a car...round filter, usually black in color.

I would change the oil first.  If that does not help I would check the oil tube dip stick o-rings, top and bottom.  Some of these o-rings leak, causeing a vacuum leak, I don't recall what model numbers, but we frequently replace them for added insurance...they're cheap.

If you still have oil burning, then check the valve breather and hoses.  Some breathers are cleanable, but they are also cheap and help control engine vacuum.  You could ask your local repair shop about the o-rings and valve breather, but many small repair shops do not regularly attend update seminar and may not know about the problem.  I know the later o-rings were changed, but as rubber parts age they become hard.

Let me know what happens...there has been a rash of oil burning questions.

As for the black smoke, this normally indicates a rich fuel mixture.  It could be the fuel you are using or the carburetor may need cleaning.  The newer carburetors are fixed jets, meaning they are very sensative to changes like small debri in the fuel system or even different fuels.

You can also keep an eye on the spark plugs.  Check them every month...they should appear to be the same color...make sure you keep them in the same cylinder they came out of...this will tell you if one cylinder is running rich or lean or the same.

Let me know if the oil change helps.
Eric