Question about Craftsman 24 Hp 48" Deck Yard Tractor

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I have a 24 hp briggs& stratton els 725 enginein a Husqvarna YTH2448 that started backfiring yesterday. I changed the air filter,the fuel filter, spark plugs, (.040 gap), and the gasoline. the backfiring occurs mostly at full throttle,runs pretty well while parked at half throttle but backfires while driving at half throttle. seems like it backfires thru the exhaust. any sugestions?

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  • rleinwi Aug 30, 2010

    Spark plug gap: B& S manual says .030,Husqvarna manual says .040. Runs good either way.

    also, runs fine on one cylinder, either cylinder.

    Not likely the valve adjustment went out of specs instantly.

    symptoms are typical of thin fuel air mixture.

    Problem was likely caused when I hose down the mower after each use, after the engine has cooled.

    could the problem be in one of the safety switches such as the one under the seat that cuts off the

    ignition if you raise up out of the seat?

    model # 446677, type: 0463 E1, Code: 050506 YG

  • rleinwi Aug 31, 2010

    I'm sure you're right. Thank you



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What is your engine model number? It will be in the form of xxxxxx-xxxx-xx.
As far as I know the 725 ELS plug gap is 0.030"
Intake and exhaust valve clearance must be .004"-.006"
Incorrect valve clearance is the most likely culprit for backfiring. This can be caused by normal wear and tear.

Posted on Aug 30, 2010

  • Rene Rossouw
    Rene Rossouw Aug 30, 2010

    According to B&S with that model number plug gap is .030" Husqvarna either have it wrong or are using a different plug than B&S. Find your model's manual here:
    enter 446677-0463-E1 in the operator's manual field.
    Have you tried pulling the choke slightly? If it is running lean a slight enrichment by way of the choke may identify the carb as the problem. You can also try a small amount of fuel directly into the carbs to enrich the mixture and see if it smooths out. If it does you'll need to get the particular carb off and give it a thorough cleaning.
    The engines are very sensitive to valve clearance. So best to double check.
    I dont believe a safety switch will cause a backfire.
    Check the plug wires to see if there is any wasted spark or arcing. It is best to check in absolute dark.



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The engine ignition can be interupted by a safety switch (seat) out of place or adjustment, or a carburetor fuel solenoid that is loosing it's supply of voltage.
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cannot be exposed to spark plug durning test !!!!
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thanks, rwvanlue

Fuel Related issues that take a certain amount of time to appear
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a) Fuel tank outlet plugged (some have a screen filter,
some are 90' angle and plug with rust and debris inside the corner of fitting)
b) Fuel lines collapse when they are routed thru fasteners and between frame and seat decks
c) Fuel cap vent clogged
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e) any fitting that has an orifice that can trap debris or rust will eventually become clogged
f) fitting on the side of the carburetor
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2) remove the float bowl fastener. This is the main jet
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4) using a spray 'carb cleaner'
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6) re-install bowl and center bolt, air filter assembly

*if you need gaskets, your Briggs dealer can supply. The kit is cheaper than individual gaskets, and all the parts needed to finish the above repair are in the kit.

I’m happy to assist further over the phone at

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