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Mend Briggs & Stratton SP460 Lawn Mower Starts Runs

B & S SP460 lawn mower - Engine hunting?

Engine starts and runs fine until warn, then starts to 'hunt' - alternating from working speed down to almost stopping then back to working speed (about a 5 second cicle). It is using more than usual amont of fuel and, strange to relate, but it started to work fine for a minute or so just before running out of fuel!

Bernard Cotton
May 2008

Briggs & Stratton Briggs & Stratton SP460 Garden Tools, Lawn Mowers Lawn Mower Starts Runs

If this is the 'carb on the tank' model, you need to replace the diaphragm between the carb and tank. It will either be holed, or work-hardened. Either way, it will be letting in excess fuel, causing the hunting. This explains the high fuel consumption, and why it started to work just before running out (no excess fuel!).

phil_saunders@bigfoot.com

Phil Saunders
May 2008

I think you'll find that the governor system is causing the up and down revving - however this won't be the fault with the engine. The problem will be a small amount of dirt or water in the carburettor which will need a good clean. There is also chance that the fuel level is too high in the float chamber so pay particular attention to the float needle valve. A clean air filter is also essential to prevent a rich mixture so its maybe worth checking this first.

John
May 2008