B&S 287707-1224 14.5 I/C OHV Wont run when hot

pscdouglasJune 7, 2013

Greetings all,

I am not a frequent browser here, but am a gardener and live close to the land. Looking forward to some good discussions with you all.

My current problem is with my mower. It was a hand me down from a neighbor for free so i couldn't resist. It has no badgeing for the actual machine but the engine is as described in the subject. I can get it started and it will run well and cut for about 10 minutes or so and then it gets rough and cuts out. It has the walbro LMT carb on it, which I have disassembled and cleaned twice. Float is good needle and seat are good. bowl gasket good. anti backfire solenoid seems to be doing its job, no problems with it and it has a good electrical contact. Spark plug is correct and good, showing signs of proper combustion and still fires strong after it dies after warmup. Valves have been adjusted to 0.004/0.006" int/exh and engine was drained and filled with new oil. New gas thru new filter and new line. Gas cap functioning properly. I am totally stumped. The block shows no leaks or excess oil consumption and the engine doesn't knock or run too fast. The cooling fins and shrouds are all in good shape and clear of cooked critters and grass clippings. I just cant seem to figure it out. Any help or experience would be appreciated. Thanks in advance!

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I'd suggest priming the carb with a couple teaspoons worth of gas when the problem occurs.
This should isolate it to a fuel delivery issue or not.

    Bookmark   June 7, 2013 at 10:05PM
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Well, I had finally got it warmed up (SO MUCH RAIN!) and running. Seems to be that this engine just likes to run rich. The plug is covered in carbon soot except right where the spark is igniting but it ran for well over an hour today as I cut the neighbors yard. Maybe the rings are just worn and this machine likes to be babied. I can even start it after i shut it down hot. Still wondering about the ultimate cause but happy that it seems to have sorted itself out. Thanks Bill_kapaun for responding.

    Bookmark   June 12, 2013 at 9:16PM
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If you feel that the plug may have heavier plug deposits- may be the start of a head gasket leak.

    Bookmark   June 12, 2013 at 10:34PM
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Did you replace the air filter?

    Bookmark   June 13, 2013 at 8:23AM
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I might try replacing the air filter- I cleaned it really well when I got the machine and it is in good (looking) condition but lacks any foam around it, it is a cartridge type. I didn't replace it right away b/c it is another $35 and I wasn't sure the machine was going to run well enough to keep. I hope it is not the beginning of a haed gasket, I looked real close at the joint, and made sure to check all the bolts to see that they were secure, but never removed the head.

    Bookmark   June 17, 2013 at 9:18PM
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I've been told that the coil could possibly be bad when our 17hp Twin 2 engine did the same thing. Seems they break down when they get hot and engine shuts off. Just a suggestion. I replaced the coil and the problem went away although now it seems to be reappearing a few years later.

    Bookmark   June 18, 2013 at 1:36PM
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well i DID replace the air filter and also decide to try and let her run a spell without it on altogether to see if I could further diagnose the problem. Seems to be kicking the fuel back from the intake. With the air filter off, I can see fuel spitting back a bit which would explain why it is running a bit rich. looks like I'll have to tear it down and replace the valve and maybe re-seat it. I'll check the rings on the piston while I'm in there and hopefully the cylinder looks ok. I really wanted to avoid tearing it up, but the rest of the machine is pretty rugged and in decent shape, seems a shame to junk it.

    Bookmark   July 7, 2013 at 4:44PM
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Spit back at IDLE RPM or at higher RPM too?
SOME spit back is NORMAL for Briggs with the compression release featured on the intake valve.
The spit back you will see on these engines at idle is nothing but the intake valve being momentarily raised off its seat when the decompression bump on the intake cam base circle rotates past the tappet. The spit back should all but disappear at high RPM.

    Bookmark   July 7, 2013 at 7:46PM
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