If I read all the posts correctly it has good spark when tested outside the cylinder but will not fire when attempting to actually start it. I had a Lawnboy mower years back that was getting the best of me. What I found was the coil insulation had broken down/cracked and the spark was jumping to ground without firing the plug.
To test, remove the engine covers to be able to view the coil and spark plug wire. Then turn out the lights and attempt to start the saw. Any spark jumping to ground will be visible.
Note: the voltage to jump the spark plug gap is increased due to engine compression as compared to the voltage required to jump a gap outside of the engine without compression pressure. In my case the spark would jump a gap with a "snap" when I tested it outside the engine. When I installed the wire onto the plug the spark would jump through the coil insulation to ground.
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Today's Featured Article - Tuning-Up Your Tractor: Plugs & Compression Testing - by Curtis Von Fange. The engine seems to run rough. In the exhaust you can hear an occasion 'poofing' sound like somethings not firing on all cylinders. Under loaded conditions the tractor seems to lack power and it belches black smoke out of the exhaust. For some reason it just doesn't want to start up without cranking and cranking the starter. All these conditions can be signals that your unit is in need of a tune up. Ok, so what is involved in a tune up? You say, swap plugs and file the points....now tha
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