Briggs & Stratton 791781 Breather Assembly Replacement for Models 699640, 495785 and 298383

Cured the engine of puffing white smoke. Easy to fit.

Very good

This product comes with the gasket, which make it a complete package, fit perfect and works like it supposed to. Gave my old lawn mower a new lease on life as I was about to throw it out due to poor idle and smoke. Lawn mower works great now.

This is basically like the PCV valve on a car engine, which is there to keep the crankcase from getting over-pressurized from the combustion process (which will naturally happen without it). It vents crankcase pressure (and oil/gas vapors) back to the intake to be burned (see the small tube that runs across the top of the block and enters the carburetor at that rubber elbow? That's the path for the crankcase venting). If it jams up/fails, the crankcase can become over-pressurized and blow out a gasket or or something.I'm going to add this to my maintenance routine-- check it every so often and probably change it out every few years. Another review on here said you can test these by whether they make a rattle when shaken (good) or not (bad). It's super easy to change, just a couple of small bolts hold it on. Some oil might come out from the valve chamber when you take it off. It needs a gasket to seal, so be careful when removing or have a backup gasket on hand. This new one came with the gasket.My mower had a number of issues, running poorly for some time and eventually culminating with the exhaust valve seat becoming unseated and keeping the exhaust valve from being able to close (and keeping the mower from starting) that finally got me to really dig into learning about and fixing this mower. Head gasket was leaking oil making me originally suspect that as the problem (after checking/replacing the air filter, carburetor diaphragm, ignition function/gap) . When I took off the head the gasket seemed ok, and anyway the exhaust valve seat problem was obvious then.Oil leak could have been loose head bolts, but could have also been overpressure caused by the bad breather valve. I re-used the headgasket when reassembling (after cleaning combustion chamber and valves of carbon crud and reseating exhaust valve seat) and it works fine. After all this (and of course new diaphragm, air filter, etc) the mower is running super well.

Item fits exactly. Lawn mower runs like new again. No more blue smoke and fouled spark plug.

My old breather assembly was mucked up and wouldn't work properly. If you shake it and it doesn't rattle, it's time to replace it. If it works fine just check the gasket which is available separately. If I understand correctly, this little device allows for the the change in displacement as the piston moves back and forth. Easy fix after you remove the muffler.

Picture shows space for vent line to carb but came with no space for vent line