helping a buddy – push mower repair

I have spent time with 3 organic growers in the area and hope to expand my circle when I am able to participate in the local Saturday morning markets.  I visit often with one grower who, tho good at growing, is less interested in repairing equipment.  His riding mower and his push mower are both out of action.  Though I use a scythe in the hilly and restricted areas, I also make frequent use of a riding mower (see my posts on various repairs) so I sympathized with him.  I tried starting his push mower with starting fluid and the engine fired and then immediately cut off.  Must be carburetion I said and suggested he could find full repair instructions on the internet.  He was not enthusiastic, so several weeks later I volunteered to fix the mower for him.

With the push mower in my basement I made a start – first thing is to find the model # and google for parts diagrams and utube videos.  But the part # related to the mower frame not the engine, so I then found the Briggs Stratton model # concealed under a shroud.  The model #  10H902 tells you a lot about the engine.  The “10” is the cubic inch displacement, the “H” is the design series, and of most interest the “9” tells you it has a vertical shaft pulsa jet carburetor.  “Pulsa jet” I thought, I wonder how it operates?  Well, with the resources of the web you can download detailed information on the pulsa jet carburetor, which is very simple but clever in operation.

here is the mower with the air filter cover removed
here is the mower with the air filter cover removed

The carburetor and fuel tank are removed as one unit.

the carburetor and fuel tank before disassembly
the carburetor and fuel tank before disassembly,  still looking dirty after I removed several coats of grime

And here is the carburetor separated from the fuel tank, with the tank mating surface facing the camera.

the red button is the primer button which you press a few times to fill the carburetor with gas.
the red button is the primer button which you press a few times to fill the carburetor with gas.

The long yellow tube is immersed in the fuel tank and when you press the primer button, gas is sucked into the carburetor.  The short silver tube interested me – what was this for?

When the engine is running, the downwstroke of the piston lowers air pressure in the carburetor and this causes a diaphragm to move which sucks gas liquid into the carburetor and also fills a little reservoir above the gas tank.  This reservoir maintains constant fuel supply to the engine because if it was not there then as the level of the gas fell in the tank, the flow of gas would be affected.  And the silver tube  sits in this reservoir and the silver color is actually a fine strainer filter for the gas.  Knowing how and where the fuel moved in the carburetor I was able to blow all the passages clean with carburetor cleaner fluid.  There are no jets to disassemble, it is a simple carburetor.  The diaphragm appeared in good condition, so, after cleaning out particles in the gas tank as well, I put everything back together again and started up the mower.  And it worked.

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