My lawn mower (has a B&S 3.5 h.p. engine) runs, but sounds like it has a miss, does not run at a constant speed. what (and how) do I check i.e. points, condenser, etc? The spark plug is brand new (less than 20 minutes running time) so I am sure that is not the problem. It is a Murray 20", B&S 3.5 hp. "classic" with throttle-free operation...carburetor was replaced earlier this season, and all ran fine till the last time I cut the grass.

Rick Maryman, September 2006

Briggs hasn't used points and condenser since the early 1980's
The only way for the engine to be "out of time" is if the flywheel key is partialy sheared. Unless you hit something hard with the blade that's unlikely. Check the condition of the air filter. Make sure the fuel is new. Another unlikely possibility is a plugged up muffler.

Rick, September 2006