earache
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Briggs and Stratton 31P777 turns over, won’t start
Hello
My Briggs and Stratton 31P777 turns over, but won’t start.
Shortly before I pulled it into the shed when I last used it, I smelled and noticed gas running out of the carburetor. I think it’s part of the carburetor anyway - an upside-down bowl-shaped metallic item, which seemed to be leaking gas from along its top edge. I turned it until the gas stopped leaking out.
it ran after that long enough to finish mowing and to be put away. Now it doesn’t start. I’ve replaced the spark plug but no difference. I know I could/should check for spark but don’t know how to do that by myself with no one in the driver’s seat.
I have navigated the Briggs and Stratton site enough to order and receive a new air filter, fuel filter and replacement fuel pump.
Advice anyone? Perhaps a list of things to try in order of relevance?
I have good mechanical aptitude and plenty of tools but very little experience with engines.
Hoping for a quick fix, I need to get these leaves up before the snow flies!
Thanks In Advance
earache
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 07:33:43
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Sounds as if the carb is your issue.
(I have almost the identical engine on my Toro zero turn).
Does the float bowl (roundish thing on the bottom of the carb) have two SCREWS on each side securing the bowl?
Or, just one bolt in the center of the bowl securing it?
There's likely a solenoid at the very bottom of either carb with two wires running off it..
That solenoid SHOULD open/retract with the ignition turned on/running. It's supposed to help with stopping "back firing" when the engine is turned off.. It's not un-common for that solenoid, over time, to stick closed-which would not let fuel flow. To check it, spin off the solenoid being careful not to loose the "pin" in the center(probably froze in anyway). Keep the solenoid plugged in (off the carb) and turn the key to "run". That pin should pull in easily-
If it doesn't move usually you can work it with a lubricant and get it moving again..
Please post back which carb you have as one (original equipment-NIKKI) is trouble some(poor design) /leaking internally is common. Mine was flooding the engine internally. I replaced with the updated carb, the Walbro..
.
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 07:34:43
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 07:36:47
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Nikki vs Walbro carbs 
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 07:40:16
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Lastly, pull the fuel line off the carb place into a container. Crank the engine over and make sure your getting fuel from the fuel pump. No fuel coming out would either be a plugged up fuel tank or bad fuel pump. This is the Nikki Carb upside down (two screws on each side of the bowl): (I replaced the PHILLIPS HEAD screws with the Allen head bolts) 
post edited by SRTsFZ6 - 2021/12/05 07:41:28
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 08:27:49
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Hey SRTsFZ6 Thanks for the swift and thorough reply! I have the carb with the solenoid on the bottom, and once it warms up a little bit outside, I will try your suggestions on the tractor and report back!
post edited by earache - 2021/12/05 08:30:43
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 10:00:22
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So here’s the latest on this Briggs and Stratton non starting problem:
I’m not getting any spark. I tried with both the old spark plug and a new one, outside of the cylinder head, with the plug held against the outside of the block and my wife turning over the engine. No spark.
Other details related to the previous posts/replies:
i have the carb that doesn’t have the two screws holding the bowl in place. Only the solenoid holds the bowl in.
I looked at a really good YouTube video about the same engine with similar issues ()
and per the video I first took apart the carb bowl and the solenoid and cleaned the jet with some wire. Solenoid and bowl cleaned back in place, solenoid clicks on first click of key turning.
The fuel pump works, supply hose off at carb and engine cranked, fuel flows to carb
I replaced the air filter.
Further ideas?
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 17:20:18
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With NO SPARK, you need to address that. Don't chase anything else... And that carb you have is the "good one".. Under the main cover is the coil, spark wire attached to that. Once there, there's a small, black wire attached to it. That is the kill switch wire. Disconnect it and re-assemble to test... If you still don't have spark, the coil is bad... If you NOW have spark, there's a short somewhere in that black wire and/or where it leads to. You can bring up a parts diagram under Jacks to see what's what/where, etc... It's not terribly difficult to get to The coil above the flywheel on mine: 
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 18:33:32
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Thanks for the info. Can the tractor run without the ground wire?
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/05 18:59:52
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earache
Thanks for the info. Can the tractor run without the ground wire?
Yep it can... When the ignition is turned off, that solenoid under the carb ALSO shuts off fuel. It'll take a knats hair longer to stop (not immediate like killing spark).. Plz post back what you find..
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/11 09:02:53
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SRTsFZ6:
I ordered a replacement solenoid, installed it and got the engine to start! Like a dope tho, I only ran it briefly, then flooded it when I went to restart it, and ran the battery down...I have it on a battery charger now and am expecting good things!
Thanks so much!
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/11 17:13:07
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 09:56:59
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Sooooo...
I have yet to get the engine running again after a brief start up (see above).
The new magneto came with a new spark plug. I have another new spark plug a direct replacement for the one that was in the engine originally (which I also still have....)
I've tried all combinations of spark plugs with the ground wire on and off the magneto, still no joy.
No one is here currently to start the engine while I check for spark.
What is the correct gap for the spark plug and what is the correct gap for the distance between the magneto and the flywheel?
If the flywheel had some rust on the surfaces at the gap, would it make a difference?
Thanks in advance
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 12:06:56
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So now, I'm truly stumped. Got the bride to try starting the mower while I held the plug on the block - no spark
Gapped all plugs at .030 - no spark.
Every combination of new and old magneto and new and old spark plugs - no spark. That's after I gapped the magneto at around .012 with a business card.
What the heck?
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 12:52:35
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I would remove the rust (not super critical) for an accurate adjustment..
Spark plug gap is .030".
Magneto to flywheel, use a standard "business card", which is about .010" between both.
There's nothing else to it so you should have spark (at least with the kill switch disconnected)
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 13:05:42
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Does it matter what I hold the spark plug against on the engine, as long as it's metal? The exhaust manifold, the aluminum of the head, it doesn't matter?
I'm going to put the new magneto back, properly gapped, and remove the kill switch wire, and try for a spark.
After that, if there's no luck, i will try some voodoo - perhaps i should kill a chicken at the crossroads tonight at midnight, or something.
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 13:06:13
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Does it matter what I hold the spark plug against on the engine, as long as it's metal? The exhaust manifold, the aluminum of the head, it doesn't matter?
I'm going to put the new magneto back, properly gapped, and remove the kill switch wire, and try for a spark.
After that, if there's no luck, i will try some voodoo - perhaps i should kill a chicken at the crossroads tonight at midnight, or something.
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 13:16:19
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Oh, ya got me laughing for the day!
Re the ground, it HAS TO GOOD and clean. I usually keep it pushed hard again the head / cooling fins.
A crappy ground gives no spark or little..
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earache
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 13:31:34
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I tried it again and no luck. I held the spark plug against several different areas on the engine to try to affect a spark, no joy.
I'm gonna recharge the battery, so that it turns the engine fast enough to generate a good spark, if it isn't already.
The kill switch wire runs back to a multi pin connector and then to - I don't know where.
If it is permanently shorted "upstream" I suppose that might be a problem that would cause no spark. True?
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SRTsFZ6
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Re: Briggs and Stratton 31P777 turns over, won’t start
2021/12/12 13:44:55
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If the kill wire is disconnected, it should spark.
Obviously, it's need to crank over fast enough.
Once you get spark back, we can chase a short/failure when the rest of the harness is hooked up
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