Your solenoid coil shorted internally.
Can be caused when people strike the solenoid with a metallic object as in "I wonder if this needs rapping with a hammer".
Or it can just short out for no apparent reason.
This is actually quite rare.
If yours looks like 629734........buy it.........cause it looks like Briggs features just 2 different ones in all the 28 series line up.
And there is a big, easily recognizable difference in the two.

I do have to wonder if your tractor has the proper amp rated fuse in place.
Usually, the main fuse is 20 amp if tractor has an electric PTO and only 10 or 15 amp if PTO is a manual engagement.
If it has a 30 that is probably too big in any case.

Of course I don't mean that a 30 amp fuse would cause the solenoid to burn up, not at all.
But I do have to wonder if too large a fuse kept the fuse from blowing in this shorted situation.

Ditto what mownie said. Especially about the fuse.

I'd never heard of this happening, but I don't work on these filthy things:)

Since you had the presence of mind to intervene in time, and actually disconnect the offending part from the source of power, I will go out on a limb and say that you are qualified to repair this machine yourself. It took some quick thinking to realize what was happening, and how to stop the small fire from turning into a big fire. I'm not sure why your Murray tractor needs to have a solenoid valve on the fuel line, but you could install a manual fuel valve between the fuel tank and the carburetor, and then you would have the ability to turn off the fuel source at any time, for any reason. I would think that if this was done, you could safely operate the machine with no solenoid in the fuel system.

Thanks for all the feedback. I was also wondering if I could safely run the mower without the after-fire solenoid. I would either need to replace the solenoid with a short bolt & gasket, or I was also thinking I could remove the solenoid, cut off the plunger, then reinstall it (without the wiring - I would remove the wiring harness from the mower.) UPDATE: Just got off the phone with my local mower shop and he has the solenoid for around $18, but does not have the wiring harness. He said he could make up a new harness if I bring him the old one. The price is right so I may just replace it.

About the fuse, I was looking at my wiring diagram, which I posted a few years back on a different post (see link below) and it shows a 15 AMP fuse between the start switch and MAIN solenoid. I assume this is the fuse that mownie was referring to. I will check and post the size of the actual fuse during my lunch break.

Also more info, this mower has a manual 6 speed transmission. I think this means it does not have an electric PTO. Thanks ALL!

Link to wiring diagram:
http://s754.photobucket.com/user/mustangm/media/42544x8bwiringdiagram.jpg.html?sort=3&o=3

Link dd not work, so uploading image of wiring diag

Actually the fuse is between the B terminal of the key switch and the battery + post.
They just use the solenoid terminal as a common mounting point.

Electric PTO (or not) doesn't have anything to do with the transmission. It just the method in which the mower deck is engaged.
It's more of a matter of cost. Manual PTO/transmissions are less expensive.

If I am reading the wiring diagram correctly, the 15 amp fuse is set up to protect the wiring from excess current that originates at the battery, only. There is no fuse protection from excess current that originates at the stator, which would be producing electricity when the engine is running.

Thanks guys for the clarification. So if I have a new wiring harness made up by my local mower shop, should I ask them to add an inline 15 amp fuse between the armature and fuel solenoid?

The PTO I refer is is how your deck blades are engaged/disengaged.
If you have an electric PTO clutch you just flip (or pull) a switch on the dash to engage/disengage the blades.
Having a manual PTO means you must physically operate some kind of large lever control to engage/disengage the blades.
Because of the extra electrical load imposed by having the electric PTO clutch, a higher amp alternator, along with a higher amp fuse is required in tractors with that feature.
Looking at this schematic, I see that a simple diode (without a regulator) is featured as a current rectfier.............that means low output charging system, hence the 15 amp fuse specification.
I also see a PTO switch, but no electric PTO clutch.
That means that THIS switch is a safety switch (part of safety interlock circuit) and functions only to kill the engine, or to inhibit the cranking motor, under certain conditions.
And to re-state for the 1,000th (or so) time.
The electric fuel solenoid on ANY outdoor power equipment is only there to help prevent the loud afterfire BANG! that can occur when shutting down the engine.
The afterfire solenoid IS NOT tasked to shut off ALL fuel flowing INTO the carburetor.
It is tasked only to shutting off the fuel flowing OUT of the carburetor MAIN JET.
When the key switch is turned off, the fuel solenoid blocks only the carb main jet, and that is how it prevents the shut down bang blues.
But, the carb pilot jet can still flow a little bit of fuel,
and that is why it is recommended to also have (and use) a manual fuel shut off valve. The manual valve, if closed at all times except when the engine is running, will absolutely prevent you from ever having an engine get drowned with gasoline during storage.
The afterfire solenoid cannot provide any protection against fuel drowning of the engine if a carb needle valve leaks during storage of the machine..........because it does not block the pilot jet.
So if you did not know why an engine has a fuel solenoid valve, maybe now you do.

Well, also looking at the schematic, I see what I personally consider to be an engineering/designer mistake in how Murray chose to connect the alternator to the electrical system.
Murray opted to connect alternator output to the electrical system by "piggy-backing" it onto the ignition switch along with the fused wire leading to the battery + post of the starter solenoid.
In my opinion, the alternator output circuit should connect directly to the electrical system at the battery + post of the starter solenoid INSTEAD of where it is shown in the schematic.
The reason I have this opinion is because..........if a short in the electrical system develops AFTER the engine is already running, there is still 3 to 5 amps of alternator output current still entering the key switch to be distributed to any circuits served by the key switch.........EVEN IF the fuse blows.
By doing the more sensible and logical option of connecting directly to the battery + terminal of the starter solenoid and leaving the fused circuit stand exactly as it is shown, would provide for no electric current from the battery, or from the alternator to reach the key switch if the fuse blows.
Engineers, as educated as they may be, do not always think in the most practical manners in all situations.
And besides, there may have been a corporate bean counter measuring the length of every wire in the proposed harness too, and the bean counters usually win because they speak dollarese while the engineers try to speak logicese.

So, yes..........you could add an inline fuse to feed only the fuel solenoid if you like. And a 10 amp fuse would be all that's necessary if you do because this circuit DOES NOT carry any of the alternator output to the battery + side of the electrical system.
Clears as 10 day old coffee, right?

This post was edited by mownie on Thu, Jun 20, 13 at 12:53

Since a fuel solenoid is supposed to draw less than an amp, I think I'd opt for a smaller capacity fuse.

In reality, your fuel solenoid shorting is a VERY rare occurrence.

You refer to the diode as a 'low output charging system.' Please let me know if I am interpreting correctly. The diode/rectifier is recharging the battery. As I follow the diagram, the charge passes from the diode to the start switch terminal, then thru the fuse, to the terminal on the main solenoid then on to the battery. I always knew that the battery gets recharged, it is nice to see how it is done in this diagram (if I am even correct).

What then, is the wire going from the fuel solenoid to the armature used for? Is the fuel solenoid picking up current from the armature?

I just went and took a quick look at the mower. The black wire from the fuel solenoid looks like it is just grounded to the engine heat shield. The white wire from the fuel solenoid snakes under the front of the engine and connects to another plastic connector. I will have to trace that tomorrow. Daughter is graduating HS in a few hours. Will post some photos of the mower tomorrow. Thanks ALL!

This post was edited by mustangm on Thu, Jun 20, 13 at 14:36

"What then, is the wire going from the fuel solenoid to the armature used for? Is the fuel solenoid picking up current from the armature?"

It really isn't.
IF you look at the fuel solenoid (on the schematic) it only has 1 wire going to it.
The other 1/2 of the connector is the kill wire to the armature/coil.
Just a matter of using a 2 pin connector instead of 2 one pin connectors.

The ALTERNATOR provides charging etc.

The armature/coil provides spark to the spark plug, just like on a walk behind mower. No power required.

Thanks for all the advice. I am still waiting for parts, but thought I would post a few pictures for your amusement. Thanks!

One more pic of the wire connector

Thank you Zed for your reply. It’s been 7 years since I had this issue and I still use this mower. I did install a fuel shutoff years ago and it has solved my issue with starting and flooding. When I am done I shutoff the fuel and let the mower run the carb dry. Not sure if this is bad for the mower, but I have not had any issues starting it since. Thanks again!

My six year old Poulin riding lawn mower did the same thing followed by FIRE flame up This is under carborator bowl next to fuel line. I was near my hose and sprayed with water at 30’ distance. is there a recall? if i had not opened the hood and my hose was not a available the fire could have been life threatening. Briggs & Straten engine This is exactly what is described in the above pod cast Remedy - remove solinoid and put manuel fuel shut off $10 cost