Hello all. I have a Craftsman model 917370561 lawn mower with a briggs stratton engine. It began misfiring, so I gave it a tune up (change oil, filter and spark plug). It continued misfiring and hard to turn on so I rebuilt the carb with the Briggs Stratton Carb rebuilt kit and also changed the primer bulb. It still misfiring and hard to turn on. I actually have to prime it 6-10 times for it to turn on and then misfires as it is on. If I turn it off and try to turn it right back up, i have to reprime which was not the case before. I then removed the filter housing and primed it and did not see any gas coming out from the tubing into the carb throttle body chamber. Actually sometimes it does come out and other times it does not. Any idea what might be causing this? Do I need a new carb or something else? Any info greatly appreciated. Thanks

 

The misfire sounds more like and ignition problem. Have you hit anything with the blade lately? You could have a keyway that is slightly bent that is throwing off the timing. It the mower is old, you may have a valve that is not seating properly.

 

LFW is giving good advice. I will add -- look for vacuum leaks. Where the carb slides onto the fuel tube there is an O-ring in carb, and where the fuel tube connects to block it has a flat gasket. Failure of either of these will let in air and mess up the air/fuel ratio from carb causing rough running and misfire. I have found fuel tubes with corroded leaks.
Check it out.
RR

 

Had this happen on my Toro mower a few years back. Prior to winter storage, I fogged the combustion chamber with SeaFoam spray. No missfire the following seaon. Appears the SeaFoam took care of a stuck valve, probably carbon related.

 

Actually for me I had no winter storage as I live down here in SFLA and mowed the lawn at least once a week... In regards to the misfire, one thing I did yesterday that I read on another forum was when I got it running, leave the air filter and cover off, then carefully partially block the air intake of the carb, and the engine ran much smoother telling me that there is something wrong with the carb. In regards to gaskets and o rings, I replaced both during the rebuild process. I guess just might be better off buying a new carb for $40 then to start getting it rebuilt by someone else or spend more money on parts. Thanks for all info.

 

The Sears / Briggs mower I have developed a crack in the plastic tube , that functions as an intake manifold . This caused an air leak that caused the fuel / air mixture delivered to the engine to be too lean .

Check that out , plus the gasket to the head and the o-ring to the carb . As some one else has said ?

God bless
Wyr

 

Which tubbing are you referring to? Can you attach a picture? I did replace the gasket on the intake side of the carb and o ring on the side of carb to motor. Thanks for info

 

This may not be the exact one , but looks like this

Briggs Stratton Intake Tube Manifold w O Ring 1193 1 2 | eBay

God bless
Wyr