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runaway engine on Briggs & Stratton 407777 0121?

I have a 46" deck Sears lawn tractor with a 20 HP B&S Mod 407777 Type 0121-E1 engine. Yesterday when I pushed the throttle lever back to the idle position the engine began revving very high. The throttle has no effect. I took the cover off and both governor springs are in place. However, when the throttle is in the idle position, the butterfly valves are still open significantly, almost like it isn't returning all the way. Nothing appears to be binding. If I manually hold the butterfly in the closed position, then it idles normally. The throttle cable is not slipping in the clamp and when it extends, everything seems to move freely. Any suggestions why all of a sudden this would happen? Thanks for any help!

Bob
September 2007

Briggs & Stratton Garden Tools, Lawn Mowers Briggs Stratton 407777 Lawn

Hi Bob,
I have the same problem after my son used the lawn tractor for hours at full throttle when I was away. My engine is 407777 0117 .
I believe the governor inside the engine block is broken as the actuating shaft that comes out of the engine to control the throttle no longer rotates as you change engine speed. Maybe you can check this. The problem is how do you get insde the engine to fix this. Through the sump or the head or some other route?

John
May 2008

Hi
I don't know if this will help, but it might.
I have a lawn mower with a Briggs and Stratton engine and there is a flap which is in the path of the cooling air to the cylinder. This flap controls the throttle position to some extent, but not completely, as there are 2 springs which act against one another. The theory is that if the engine gets loaded, the rpm decreases, the ammount of air cooling the engine decreases, and so the flap tries to move the throttle to a more wide-open position. Check to see if you have such a flap, and see if it's free to move, it could be holding the throttle open too far.
Jack

Jack Rogerson
September 2007

If you want to replace a new engine with this Sears Craftsman 917.270750 917270750 Briggs and statton 407777-0121-E3, visit:

http://engine4less.com/shop/product.php?productid=17489&cat=0&page=1

Or visit http://www.engine4less.com.

MMM
September 2007