Briggs started backfiring, lost power and quit.

bfield3

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I apologize if I have double posted. I'm unable to find my original post.

It may be time to just get rid of this mower, but I was hoping to finish out the year with it. So hopefully someone has an idea on what's going on.

Anyways, my wife was cutting the grass last week and ran out of gas. She put gas in it and couldn't get it re-started. I then tried to get it started and had no luck. Turns out I wasn't getting any spark. So I removed the magneto or armature (whatever it's called) and cleaned the part that passes by the magnet on the flywheel. Also cleaned the magnet on the flywheel. Still no spark, even when I took the grounding wire off. So I ordered a new magneto. After putting that on the new magneto and also putting in new plugs I was now getting a nice spark. So I thought I had it licked. Well - the dang thing still wouldn't start. Spun over easily and seemed to have good compression. Was getting fuel. After monkeying with it for quite a while, my wife says, what can do you keep the gas in? I pointed to it and she said "I didn't use that can, I used this one". "This one" just happened to have kerosene in it. Ugh....Well at least I now know what the problem is. So I emptied the kerosene out of the system, cleaned the tank, fuel lines, removed the carb and cleaned that. Basically got all the kerosene out of the system. Then I filled it with gas and it fired right up. Thing ran great for about 20 minutes. Then it started backfiring and losing power. Finally it quit and wouldn't start again. Back into the garage and when I checked for spark I have no spark on both plugs again.

I'm at a loss. Is it possible my new replacement magneto has gone bad? I'm wondering if it was backfiring because initially one of the plugs wasn't getting any spark and it finally quit when both stopped getting spark. I plan on taking it apart again, but before I do I was wondering if anyone might have an idea.

It's a 17 HP B&S twin cylinder. It doesn't have points or condenser or any of that stuff. Just the magneto to generate the spark. It's at least 12 years old so maybe I need to break down and buy something else. But as I mentioned I was hoping to finish out this year with it.

Thanks,
Bill
 

ILENGINE

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If the magneto has failed again I would be checking for a bad key switch that is possibly let 12 volts get to the magneto and frying it. Before I replace the mag again I would put a multimeter on the wire coming off the mag and then switch the key on and off several times and if you get voltage once then the key switch is bad and needs replaced along with a new magneto which Briggs wouldn't warranty due to a faulty key switch.
 

SONOFADOCKER

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If it has the electric wire that goes to the bottom of the fuel bowl - it is an anti backfire module - it is designed to shut off the fuel when the key is turned off so you do not get the back fire explosion in the muffler .
If the wire was damaged during your maintenance or it is loose it can be shutting off the fuel going into the carb .
No starts occur from any safety feature that is dirty or broken . Seat,brake,pto safety all will stop fuel delivery or spark .
 

bfield3

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Thanks guys....I'm gonna have to keep digging. Weird thing is if I let this set for quite a long time it will start right up and run fine for about 20 minutes. Then it starts backfiring again and loses power and quits. Almost like something is heating up.

So I ended up putting the old magneto back on and it ran great for about 1.5 hours. Then I shut it off to do something else for a few minutes. When I tried to start it again it wouldn't start and once again no spark. I'm sure if I wait long enough it will start again...

Oh well...maybe I'll get lucky and as long as I get it started it will stay running long enough for me to get the grass cut a few more times this year. Then it's out the door for this thing :)

Thanks again,
Bill
 

beendunned

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The "ran for twenty min. then quits", brings to mind a repair bulletin, about gas tank filler caps vent plug blocking up and causing fuel stoppage, because of negative pressure in the gas tank. try loosening the cap after it stalls, and A) listen for a slight hiss of air, or the plastic tank slightly changing shape, or B) clean the cap, or buy a new cap. It's a long shot but sometimes it's the simple things. good luck
 

marvxyz

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The "ran for twenty min. then quits", brings to mind a repair bulletin, about gas tank filler caps vent plug blocking up and causing fuel stoppage, because of negative pressure in the gas tank. try loosening the cap after it stalls, and A) listen for a slight hiss of air, or the plastic tank slightly changing shape, or B) clean the cap, or buy a new cap. It's a long shot but sometimes it's the simple things. good luck

You also could have a wad of debris in your gas tank which allows gas to flow to a certain point and then cuts it off. (experienced it)
 
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