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Craftsman LT 1000 backfires no start

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2025/07/11 13:01:07 (permalink)
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Craftsman LT 1000 backfires no start

Got a new house and bought a used LT1000. It ran fine for 2 months and then it started running rough and backfiring. It now backfires and will not start. Here is what I’ve done so far:
- replaced the carburetor
-replaced the plug and validated there’s spark
- adjusted the valve clearance
- replaced the fuel filter
- confirmed the flywheel key is intact
- replaced the fuel filter

What else can it be?
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    SRTsFZ6
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    Re: Craftsman LT 1000 backfires no start 2025/07/11 17:34:38 (permalink)
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    What BRAND ENGINE, what HP, what MODEL # of the engine???
     
    Previous history???? (Just got it, sat in the rain, etc)
     
     
    .

    Scott
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    Re: Craftsman LT 1000 backfires no start 2025/07/12 18:22:18 (permalink)
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    It’s a Briggs Stratton 18hp OHV Intek engine. 31H777-0605 E2 050701ZD

    I don’t know the previous history but it ran fine for a few months then sporadic backfiring with pulsating idle. Last week it got worse and it now no longer starts and backfires when I do try.
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    SRTsFZ6
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    Re: Craftsman LT 1000 backfires no start 2025/07/13 06:15:14 (permalink)
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    https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/briggs-stratton/briggs-stratton-engine/200000-399999-series/31h700-to-31h799/31h777-0605-e2 
     
    Does it backfire thru the exhaust or intake?
     
    Have you checked the valves, that their opening and closing and what spec 
    ( in thousands) are they set at ) ?
     
    Will it fire off with a spritz of carb cleaner down the intake when cranked over?
     
     
    .
     
     
    .
    post edited by SRTsFZ6 - 2025/07/13 06:17:52

    Scott
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    Re: Craftsman LT 1000 backfires no start 2025/07/13 07:18:45 (permalink)
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    I did set the valves to the appropriate specs. I think it was .004 and .006.

    It backfires thru the intake. I tried starting fluid and it backfired.
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    SRTsFZ6
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    Re: Craftsman LT 1000 backfires no start 2025/07/13 14:39:24 (permalink)
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    Seems the intake is not fully closing or is out of time.
     
    Can you do a "leak down test"?   
    A compression test too, but the leak down would be more conclusive..
     
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    Scott
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    Re: Craftsman LT 1000 backfires no start 2025/07/13 19:07:49 (permalink)
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    I don’t have the equipment to do a leak down test. I’ll do a compression test. I spent $500 on the mower. Not sure how much more money I want to throw at it.

    I was hoping it was something easy and restively inexpensive to fix.
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