any one out there know how to fix lawn mowers?
what are the most common problems of a lawn mower not starting? how much compression is there? can you feel the compression if you plug the hole with your finger and crank the engine? how can you test the coil?
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In my experience, the most common hard starting problem is stale fuel left in the fuel tank over the "off season."
As the fuel evaporates it tends to clog the small galleries [passages] inside the carb and creates fuel "starvation" when trying to start or run. IF this is the problem it usually requires dissembly and overhaul of the carb.
IF you're lucky you may correct it by pouring all the stale fuel out of the tank, and refilling with fresh fuel to which you've added some Carburetor Cleaner or Fuel Injection and Fuel System Cleaner, both of which are available at any auto parts supply store.
As for compression, you "feel" it quite well when trying to crank the engine while pulling the starter rope handle. Compression causes the resistance you feel. But yes, if the engine has good compression, then during that cranking test the compression will be felt with your finger, and PROBABLY will "blow" air past your finger. You generally cannot "hold back" the compression of any engine.
Even with an electric start engine you can sense the difference by how labored the cranking is with the plug in compared to when the plug has been removed. There will be a difference in the SOUND, and also in the speed at which the engine turns over during cranking.
Most ordinary mower engines do not have a coil, as the spark is created in the Magneto. To test for spark, remove the spark plug, attach the spark plug wire back to the plug, and hold the plug threads tightly against the engine metal to ground it. To reduce the chance of getting shocked, hold the plug with a well insulated pair of pliers, AND WITH a leather glove on your hand.
Then while the plug is grounded, crank the engine and look for intermittent sparking in the "gap" in the plug. Depending on circumstances, is MUCH easier to have a second person helping during the plug spark test.
To tell if there is a lack of compression problem, turn the engine over by hand with the spark plug IN. Then, remove the plug and crank the engine again. Without the plug installed, there will BE NO COMPRESSION. By comparing the difference in the two tests you can tell if there is a problem.
IF it is just as easy to crank with the plug IN as when the plug is out, then there is a problem of lack of compression. I doubt you have that as unless an engine is totally "worn out," there is always compression.
the most common problem is old gas and dirty carburetor. (ie dirty air filter, water or sediment in the bowl, Your coil emits the energy to generate the spark. If it is working you will have spark at the plug. Just pull the plug and insert it into the spark plug wire, and pull cord. You should see it but you may have to shade it. If it is very faint you should try another plug. You can tell compression if it resists went you roll it over (with spark plug in). but someone you know should have a compression tester. However I would check all the normal maintenance stuff first and try to get it running.
most times the problem I had was a gas fouled spark plug. You can try removing the plug and cleaning it or put in a new one and see if that is the problem. Easiest to check and to fix before looking at other things.
if your carburetor has a small bowl on the bottom,remove it(with gas off)it should be a half inch wrench. clean it out, let some fuel run through by turning gas on for a bit, replace it.now remove the plug and check for spark as described earlier.you may want to take sandpaper or emory to the magnets on the flywheel under the starter as well as put around 3 to 5 drops of light oil into the top of the starter clutch(it has a small hole in it). anyway if you have no spark, check to see that its not the plug, if its got a good plug, then trace the black wire coming from the mag(black thing with metal ears and to small bolts coming out of it and spark plug wire attached)make sure it is not chaffed and that its ground terminal in the throttle linkage is clean and working.(if its disconnected, and you spin the motor over by hand it should spark.if it doesnt when connected, it may be a ground in the little kill switch.if your mag has 2 small black wires and 1 goes under the flywheel, then youve got points and the flywheel must be removed to service points and condenser.anyway ill stop there, this is routine every spring along with sharpening or replacing blade.