Articles: Lawn Mower Repair

Small engine coils rarely go bad or fail to function on single cylinder engines,although twin cylinder engines seem to have more of a problem, especially briggs.The flywheel has a magnet attached to it in a certain spot and as it passes by the coil,it causes the coil to charge and send a spark to the spark plug.There are no power wires going to the coil.The only wire on todays engines attached to it besides the spark plug wire is a ground wire that is attached underneath coil and it runs through usually a safety switch circuit on lawnmowers or a cuttoff switch on other applications.However if a power wire gets attached to this ground circuit by mistake it will blow the coil.Ihave seen this before, also it will smoke or burn the hot wire that is attached by mistake.Older briggs and tecumseh have a set of points and condenser that are located underneath flywheel and usually that was a yearly chore to replace points and condenser, but todays engines use an electronic coil that does away with the points and condenser.You also can replace old style coil that has points with electronic coil, by simply bolting it on.TROUBLESHOOTING COIL is simple by disconnecting ground wire, which is usually black coming from coil,pull plug out, spin engine and watch for spark, no spark, bad coil, good spark, good coil assuming spark plug is good.You can bypass safety switches with this method also,engine wont shut off until you connect wire back though.Briggs coils from one engine to another as far as horsepower wise usually wont interchange, it all depends on the size of flywheel  in bigger horsepower engines.A SIGN of a coil going out will be that the engine will run until it gets hot and then shutdown and when it cools will fire back up and do the same thing,do the above test when its hot to check for sure that it is the coil failing.Coil gap is .010 between flywheel and coil.
Small engine wiring is relatively simple from 3hp to 20 hp.Take for example the old style briggs 12 hp without overhead valves.There are usually two wires coming from underneath the flywheel cover or cap,one is the charging wire, which comes from the alternator and it is located underneath the flywheel, it charges the battery thru one of the wires coming from underneath the flywheel cover.The other wire usually a black wire goes to the coil as a ground wire and serves to shut engine down when you turn key off, it also winds its way through your safety switches.These are actually the only two wires on a 12 hp, unless it has a fuel shutoff solonoid underneath the bowl of the carb, which most of todays engines have.The latest engines are mostly overhead valve with this fuel shutoff solonoid on the bowl,which is an added two wires to the engine,so now their are four instead of two.The fuel shut off solonoid will have usually a grey and black wire going to it, the black is a ground and the grey is a hot wire, when ignition is turned on.I f your battery is dead and you try to jump engine off, most likely it will run until you take jumper cables away,because the fuel shutoff solonoid needs a good battery to operate.I MYSELF usually by pass this solonoid by unscrewing it from the carb and snipping the pin off even with threads, when I FIND IT BAD.It is a shade tree method of getting out of spending 30 to 40 bucks for a solonoid.I ALSO INSTALL A cuttoff valve between tank and carb so I CAN CUTT FUEL OFF FROM ENGINE WHEN NOT RUNNING.In actuality a lot of troubleshooting can be performed,by disconnecting the wire to the coil, or ground wire, not spark plug wire. For instance if your engine spins and does not fire, you can disconnect this wire,and if it fires and cranks it tells you that you have a bad safety switch,since ground wire winds its way through those safety switches.The wiring on a small engine rarely gives any trouble,most of the time its the wiring on the frame of the mower or what its powering.Safety switches are usually the problem associated with not running.TIP;Indication of a bad ignition coil would be, if you disconnect the ground wire talked about above and the plug will not fire with a plug you know is good, is a good indication the coil is bad, also an engine that will run until it gets hot and shuts itself off and the when engine cools, cranks back up is another indication coil is going bad.More information on safety switches can be found in my troubleshooting guide at http://pass smallenginetrblshtng.com