Cant get a spark on my briggs and stratton 4hp engine, trying to
Engine bee stood for some time.plenty of compression, also magneto on top of flywheel has moved and do not know the gap.
I just finished rebuilding my 8hp magnetron briggs which is on my pto horse, repainted all while it was apart. I had it bored 10 over, valves ground,when I got it all together no spark. Just installed new coil, took head bolt out cleaned it to insure ground to block no help. I had to do that to the starter too.
Re: cant get a spark on my briggs and stratton 4hp...
Doooh!!!! had the coil on backwards this will cause a weak or no spark situation. Should have had my glasses on , there is a faintly perceptable this side out on the new coils. Also there is no mention of this in the directions.
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Check the engine stop wire where it connects to the carb mounting plate. make sure it is not shorted to ground. Remove the top cover from the engine and check the flywheel to magneto air gap, it should be about .020 of an inch, this is about the thickness of a matchbook cover. Also check the spark plug wire and the connections, make sure they are clean and tight. The magneto is the y shaped piece behind the flywheel. Remove the flywheel holdown nut and washer and make sure the notch in the flywheel and in the crankshaft are across from each other. If they are not, you will need to remove the flywheel, and replace the aluminum key that goes there. The notches need to be aligned for the ignition timing to be correct. I hope this helps, good luck. Dan
There are 2 things that cause backfiring.
1. Dirty valve seats where the valves are bypassing compression
2. The engine flywheel key partially sheared or sheared and the engine is firing out of time.
Do a compression test. You should have 110 minimum PSIG indicated but 120 + is desired. I think you will find there is a compression problem.
If the compression is good use 2 new spark plugs and attempt another start. After the spark plucg change the wiring to the magneto and the magneto to be tested.
If you can not tdetermine the problem I need your exact engine model and type numbers (ALL of it) so that I can get you service manual data to assist in repairs.
I believe your problem is not the coil/magneto but rather your timing. If you hit something hard with the blade you most probably sheared the timing key. This key is what keeps your flywheel in the proper timing position. Remove cover top of engine, remove flywheel bolt,remove flywheel, remove key. If key is sheared off or even dented replace.Put back together. Happy mowering.
It all depends on the model of engine. If it is a twin engine doesn't it have two magnetos.Very unusual for both to go bad It will depend on the type of ignition(points or solid state) The wire going to the magneto could be the kill switch (kills when grounded) Disconnect it and see if you get spark. IF so then it is in your safety/ignition circuit. If you replace magneto usually the gap is .008-.012
The magneto is by the flywheel. Depending on the age, there maybe points under the flywheel. If so you remove the flywheel and there the points are. Sometimes bugs build cacoons between points, make them inoperable. Newer engines have electronic ignition though. Follow the small wire from the magneto coil ( where the spark plug wire goes) it will either go under the flywheel through a plastic bushing, or to an electronic module. The magneto coils do fail you can test with an ohm meter. Before that test for spark. You can remove the spark plug, and let it rest on the engine to get ground, and turn the engine over. You always need 1-spark, 2 fuel . If you have spark, see if it will hit on starting fluid, if it does, then you have a carb or fuel filter issue. Those shut off valves on the bottom of those tanks, can be a problem
Did you sand the rust off of the flywheel? where the magneto is. And did you set it right? It has to be real close to the flywheel. The thickness of two pieces of paper. And yes the pto switch will keep it from starting. If it is ingaged it wont start. Can you hear it enganging when you connect the battery? Try turning switch on and off see if it will kick in and out. With key on
gap from coil to flywheel is .010. if you've replaced coil, points and condenser with no spark i would try replacing the coil and points with an magnetron kit or a coil that allows for the elimination of points.