Snapper w/ Briggs 286707 12.5hp surges when riding - Lawn Mower Forums : Lawnmower Reviews, Repair, Pricing and Discussion Forum
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post #1 of 5 (permalink) Old 06-15-2019, 08:53 PM Thread Starter
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Snapper w/ Briggs 286707 12.5hp surges when riding

So I've replaced a lot of parts on this Briggs 12.5hp since I got this Snapper from a friend. Where it sat outside for a couple years. I've done all the maintenance including cleaning the cylinder head which wasn't really too bad. I replaced the carburetor, filters, cleaned the fuel tank, put a new filter, plug, starter clutch, rewind spring, throttle cable, adjusted the throttle control lever, coil. It actually will run and mow without cutting off anymore but it surges every couple seconds. It seems to be more noticeable at fast speed. It starts up real easy, usually with just a single pull. It feels strong, just has a hiccup every couple seconds that you can hear. I'm guessing it's considered a miss. I thought maybe the flywheel key was sheared but it wasn't. I replaced it when I changed the starter clutch. I will say that I thought maybe just the mixture on the carburetor is off. But when I go to adjust the mixture screw and it's suppose to stumble when you turn it all the way in it never does. Actually turning the mixture screw doesn't seem to affect it either way, at least in idle. It's like it has no affect, so it's hard to adjust. Any ideas?
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post #2 of 5 (permalink) Old 06-16-2019, 05:33 PM
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Quote:
Originally Posted by wh23g3g View Post
So I've replaced a lot of parts on this Briggs 12.5hp since I got this Snapper from a friend. Where it sat outside for a couple years. I've done all the maintenance including cleaning the cylinder head which wasn't really too bad. I replaced the carburetor, filters, cleaned the fuel tank, put a new filter, plug, starter clutch, rewind spring, throttle cable, adjusted the throttle control lever, coil. It actually will run and mow without cutting off anymore but it surges every couple seconds. It seems to be more noticeable at fast speed. It starts up real easy, usually with just a single pull. It feels strong, just has a hiccup every couple seconds that you can hear. I'm guessing it's considered a miss. I thought maybe the flywheel key was sheared but it wasn't. I replaced it when I changed the starter clutch. I will say that I thought maybe just the mixture on the carburetor is off. But when I go to adjust the mixture screw and it's suppose to stumble when you turn it all the way in it never does. Actually turning the mixture screw doesn't seem to affect it either way, at least in idle. It's like it has no affect, so it's hard to adjust. Any ideas?
sounds like that carb is bad, even if it was replaced with new one they can have issues right out of the box new.

get a new carb for it here https://www.ebay.com/itm/NEW-Carbure...ss!70068!US!-1

and that will fix all your problems. be advised though that those new mass produced carbs now come without the screw setting pre-adjusted correctly so you will need to double check it and lightly seat it all the way in and back it out 1 1/4 turns, then install the carburetor with a brand new fuel line the whole way. fuel lines can get spongy and swell internally and be blocked while still looking good on the outside.

You can only learn if you ask the question, so there are no dumb questions.
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post #3 of 5 (permalink) Old 06-16-2019, 08:09 PM Thread Starter
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How do I know if the governor is out of adjustment? I originally tried to replace the governor spring because the old one looked kinda weak. But I put the new one on and it seemed weaker, like it was the wrong one. I ordered it from ebay from a mower parts seller who claimed it was the number I needed but it didn't come in a Briggs sealed bag. So it could be the wrong spring. With the new one I couldn't get the choke plate to close all the way. Now I put the old one back on and tightened a bit by bending the end and the choke closes when you put the throttle on choke. It starts right up easily, when you put on slow it idles, and when you move it to fast it speeds up. All the rpm specs seem to be right on. It's 1750 at slowest setting and 2800-3000 at fast idle. I think it should be 3400 max at fast idle. My governor has the tang you bend to adjust it. That's only adjustment I know of. But maybe I need to order a new spring.
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post #4 of 5 (permalink) Old 06-19-2019, 05:59 AM
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I just had a very similar issue with the same mower and engine. I was stumped and I finally took the new carb off, took it apart (it was ordered on Amazon) and found 2 o rings where the float goes into the base of the carb. There should only be 1 o ring there, it is about 1/4" in diameter. Put it back together and runs like a champ.

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post #5 of 5 (permalink) Old 06-19-2019, 10:02 AM
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If there is a governor adjustment try that. I had the very same thing happen on my Lawnboy and once I figured it out it ran like a champ. FWIW - the Lawnboy has a small white wheel at the base of the governor fine/vane which you can spin spinned, it will go in either direction, so you will have to try both directions until the surge goes away. Once I found this out I was a happy grass cutter. I hope this works.
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