Craftsman 917-270514 Knocking, Spitting, Sputtering, Backfiring - (photo/video)


Old 07-27-13, 08:44 AM
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Question Craftsman 917-270514 Knocking, Spitting, Sputtering, Backfiring - (photo/video)

I have a 1998 Craftsman 42in riding lawnmower (Model: 917-270514). It has been a good one! However, this week, it started to "knock" hard (only term I can think of to describe the sound) when running. It also spits & sputters and backfires loudly.

The mower will start right up, and with some coaxing of the throttle, stay running. But, the shimmying from the knocking & backfiring sound dangerous. There is NO smoke associated with the backfiring - which I find odd.

So, I need a little help. I have a video of the engine running (link below). Also, and this could be very important -- a photo of an oddball plug that doesn't seem to fit anywhere.

THANKS for your help folks!

Briggs & Stratton 14.5HP OHV
Model 287707
Type 1255-E1

A video of the engine running - knocking, spitting, sputtering - is in a shared folder on my Dropbox:

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Old 07-27-13, 10:56 AM
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I saw the video. Try a new spark plug.
Old 07-27-13, 01:26 PM
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Sounds to me like the carburetor is leaning out.
Old 07-27-13, 06:58 PM
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Bet if you rebuild and clean the carburetor it will stop doing it.
This type problem as been a big issue ever since they forced ethanol fuel on us.
Run non ethanol or buy some of the additive to counter act the effects of it.
Old 07-28-13, 05:12 AM
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THANKS folks. I'll clean the carb, replace the spark plug and buy the gas additive.

Just asking... It is not odd that the mower ran for more than a decade without this problem? I replace the spark plug regularly and we have always purcahsed gas from the same country store.

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