Many people would consider running a compression/leakdown test at this point, certainly.First, try this. Get a known good spark plug. Bend the electrode out to about 3/16 inch. Clamp the plug securely to a surface like the engine block. Now, pull the wire off each cylinder in turn, and connect it to the special plug. If you mix them up, remember: firing order 1-2-4-3. Do them one at a time and you CAN'T mix them up. Each cylinder should have a nice, fat, bright blue spark. If you get weak or discolored spark check the way the plug is clamped to ground and try again. A narrow or discolored spark can make an engine miss under load. If the tractor passes the spark test, you can run a compression test. If it passes the compression test, I'd get a flashlight and a dentist's mirror and check for rust in the tank, especially if the tractor is kept outdoors.
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