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But first to see the spark plug is firing by removing, grounding to the cylinder where you can the gap then pull the starter cord.
If there is spark jumping the gap then your more likely to have a compression problem. These engines needs at 100 psi to fire; otherwise, fuel is just drawn in but is never ignited by the plug.
In this case you would remove the muffler and check the cylinder, piston and ring condition . A bad scored cylinder or piston will cause lack of compression. A struck ring will also cause lack of compression. A struck ring can check for by using a small screwdriver gently probing the ring to see it moves freely. If the ring is struck then the cylinder will need to removed so ring and piston can cleaned. Note: these are easily broken so don't use to much force when trying to free them.
A lot of times i see in here "my car won't start" or "I put new plugs in it and it still won't start". If it is petrol engine you need fuel (gas at the right mixture with air) in the right amount, a spark at the right time compression in other words the when the piston comes up to the firing time the valves are closed and there is no air escaping past the piston rings or blown head gasket ( low compression). If one of these things isn't happening it won't start. It is a process of elimination, Check for spark then gas then timing, you may have a spark but at the wrong time and last of all compression test, most engines won't start under 60 lb psi.
ok did you check to see if the spark plug wire is good and if it is good take out the spark plug and put it on the spark plug wire that its not firing on if it fire at the spark plug then you should do a compression test if the compression is bad you may have a burn valve or something and that would be what causing the misfire
You did not indicate whether or not you have compression now that you have changed out the gaskets and piston rings. If not, it seems to me that the problem could be a) cracked head or block, b) bad valve(s) or even c) a warped head.
Could be low compression (poor piston rings) or plugged air filter.
If it looks like oil on the plug, not fuel, you could have a crank seal issue, as the right side one will **** in transmission oil if it leaks.
#1 cylinder not firing, check spark plug, spark plug wire, remove spark plug and use a compression tester, and check the compression of that cylinder. should have at least 65 pounds of compression per cylinder. If the compression is low, you may try shooting a little oil in to that cylinder, replace spark plug, and try running motor again. if the compression is low on said cylinder, could be due to bad piston rings. requiring a motor rebuild.
Have you measured the compression? Very low compression can be the reason. And the reason for low compression can vary - broken compression ring, worn valve/valve seat... You are sure you are getting a spark, just before the spark plug, right? Have you checked the timing of ignition?
Four things I can think of: 1) There is a short in your spark plug wire. When you bend it to connect the plug in the machine it allows the exposed cable to contact the engine block. Examine the wire all the way to the coil.
2) Flywheel key is sheared ( you obviously know how to take off the flywheel since you checked the seals).
3) Flywheel air gap is not set correctly. Loosen the coil. Put the cover of a notebook or the cardboard piece of a cigarette pack between the magnetic portion of the flywheel and the coil. Tighten the coil down. This will get you the proper gap.
4) Your cylinder/piston or rings are scrubbed out. Even though it passed a compression test, on rare occasions it will loose compression only when it fires. So do the following:
Remove your exhaust manifold. Look into the cylinder with a flash
light. You are looking for scratches. Anything larger then a light
fingernail is definite proof you need a new cylinder/piston assy.
If it passes that test do the following:
mixed fuel straight into your cylinder until 1/4 full. Slowly pull your
saw over while looking into the cylinder. If you see bubbles after the
ring/rings go by then you need a new cylinder/piston assy. On rare
occasions if no scratches are present on the cylinder wall or piston,
you may be able to change just the rings.
First if you can get a inline spark tester so you can see if your getting spark with the plug installed.