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bgsengineclinic
bgsengineclinic, Small Engine Technician
Category: Small Engine
Satisfied Customers: 220
Experience:  Over 20 years of experience in Small engine repair, Kohler Certified Expert Technician, Self-Employed in my own dealership.
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I have a lawnmower with a Briggs & Stratton engine model 120000

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I have a lawnmower with a Briggs & Stratton engine model 120000 that keeps oiling the spark plug. Also even after cleaning/replacing the spark plug it will chug a few times, never really run before stopping all-together. Any way to adject it?

bgsengineclinic :

OK keeps oiling the spark plug as in it gets covered with motor oil?

bgsengineclinic :

Have you checked the engine oil level? - is it a dipstick or just a filler plug down on the base?

bgsengineclinic :

spark plug turns black or just gets fouled with motor oil? smokes when it runs?

bgsengineclinic :

there are multiple possibilities, so I'll work with you to eliminate or confirm some of the most common issues. If the engine oil level is overfull (they take 18 to 20 *ounces* of oil to fill properly) it will pass oil into the combustion chamber and out the breather, plugging the air filter - once the paper air filter gets soaked with oil, it is no good anymore.

bgsengineclinic :

if the air filter is paper and soaked with oil, it will cause the engine to run rich and spit black smoke and chug along and turn the spark plug black

bgsengineclinic :

if the mower was tipped on its side to service or sharpen the blades, this will cause oil to leak into the combustion chamber and breather, and also get into the air filter, depending on which side it was tipped on. In this case, just verify engine oil is full and you'll need to replace air filter, and then you'll be able to run the engine, it will smoke a while and then stop smoking and run just fine.

Customer:

Engine oil level is at full. Spark plug turns black and when I remove it the thread is oily. Yes, it smokes when it runs. Just cleaned the air filter and no evidence of oil there.

bgsengineclinic :

OK spark plug turning black and chugging generally indicates rich fuel mixture - what is the background to this, when did it start ?

bgsengineclinic :

a sheared flywheel key from something as simple as a loose blade or hitting a particularly heavy clump of grass or a root or rock can cause the ignition timing to be off enough that it runs but does not run right.

Customer:

Had it serviced a couple of months ago, because of this very problem, and all was well until a cord got wrapped around the blades and it started the problem all over again. Checked the manual and it says "carburetor is not adjustable". I must be getting a spark initially as it chugs a few times before stopping. Any way to open, clean or ?? this engine?????

bgsengineclinic :

OK - It sounds very much like a sheared flywheel key , and also as I mentioned, tipping the mower on its side to remove that cord can load up oil into the combustion chamber

Customer:

Ignition timing - where and how do I find/tackle this?

bgsengineclinic :

does it smoke, and what color is the smoke?

Customer:

smoke is black

bgsengineclinic :

ignition timing involves simply removing the blower housing and the flywheel - if the key is sheared- - can remove the nut on the flywheel, remove the washer and cup, and look down and you will see the key

bgsengineclinic :

the grooves in flywheel must line up perfectly with the groove in crankshaft , if it does not, the key is sheared.

bgsengineclinic :

black smoke indicates too much gas then, so it isnt oil problem

bgsengineclinic :

too much gas or timing is off

bgsengineclinic :

carburetor is indeed not adjustable so it is either leaking at the inlet needle, or the ignition timing is off

bgsengineclinic :

I strongly suspect it is the sheared key, since cord wrapping around the crankshaft can indeed cause that - especially if it made the engine stop quickly

bgsengineclinic :

carburetor can only be cleaned and replace gaskets - unlikely to have had that issue appear suddenly just from stalling out. float needle could have debris under it allowing gas to leak out, but it would also leak into the combustion chamber and contaminate the engine oil - causing oil to be slightly overfull, and thin, and smell like gas.

bgsengineclinic :

gas in the oil is bad, and needs oil changed, if that is the case

Customer:

OK, does this mean an adjustment of the sheared key or replacement?

bgsengineclinic :

replacement - keys are cheap - part # XXXXX is a $1 to $2 part

bgsengineclinic :

and it is quite common - most any mower dealer has them in stock

bgsengineclinic :

Briggs & Stratton 222698 , they also come in a DIY 3-pack #5002K or #5002H

Customer:

OK, will try to tackle it. Thanks.

bgsengineclinic :

if you have the flywheel nut off, you just need to tie down the blade safety handle on the mower handle and use a simple 2-bolt puller in the holes in the flywheel to remove flywheel -

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