How to Turn the Idle Down on a Model 917.378770 Briggs & Stratton Mower

The Craftsman model 917.378770 walk-behind lawnmower sold by Sears is equipped with a Briggs & Stratton seven horsepower gasoline engine. The carburetor on the Briggs & Stratton has an idle-adjustment screw that conserves fuel and helps the engine run smoothly when the mower is stationary. The idle screw also prevents the throttle plate from closing completely so the engine does not shut down. Turning down the idle takes only a few minutes using common tools and a digital tachometer for two-cycle engines.

Digital tachometer
Screwdrivers

Instructions

- 1
  Shut off the mower engine and allow it to cool completely. Remove the wire and rubber cap off the tip of the spark plug at the front of the engine.
- 2
  Remove the screw in the center of the five-sided air filter canister and lift the parts off the engine to expose the carburetor.
- 3
  Attach the clip on the end of the digital tachometer wire to the tip of the spark plug on the engine and slip the spark plug wire onto the tip of the plug.
- 4
  Start the lawnmower engine and recruit a friend to hold the kill-switch lever on the handlebars in the up position to keep the engine running while you adjust the idle.
- 5
  Insert the tip of a flat-blade screwdriver in the idle screw on the carburetor and turn the screw counterclockwise to lower idle speed. Briggs & Stratton recommends a setting of 1,750 RPMs (revolutions per minute) for the two-cycle engine installed on the Craftsman lawnmower. Check RPMs on the tachometer as you adjust the idle screw.
- 6
  Release the kill-switch lever to shut off the engine.
- 7
  Reattach the engine air filter with the screw.

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