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mower starts when cold, stalls when hot. has been tuned up, can it be the coil? was told that it was wet gas

Mechanic said that it was water in the gas... the tank has been emptied, the carb cleaned, new plug, and new blade. It still stalls after about ten minutes of running, and then may start back up when it's cold.... I've been thinking that it is a coil problem.. That's the only thing left unchecked because it fired up at the shop , so they sent it home.... And I am curiouse to know a safe way to check a coil while the engine is hot... I have a multimeter, I just don't know how to use it on a coil , or what readings I may be looking for. Thanks for any advice I can get Slacker

Had this problem, took cerberustugowar's advice, was the cap...............that I had traded off another mower 4 months ago when It was doing the same thing and I figured this one out on my own........Im getting old.
Forsure it can be the coil. But you need a tester that can take the high voltages. The shop that you took it to should have a tester there and it should only take 1 minute. You can also check it yourself. Check it when the mower is cold by removing the sparkplug, putting it back into the sparkplug boot and resting the metal part of the sparkplug onto the cylinder of the engine. Make sure it's a nice strong looking blue spark. Try this same test after the unit has quit on you. If it was the carburator it would be a constant problem. as long as everything was cleaned out and all old gas and debris was removed then it should be good. gaskets and the intake track shouldn't change during heat up and cool down. This would also be a constant problem. If the flywheel key was sheared then the unit would not start or would constantly run poorly. How does the mower stop running, Does it stop suddenly, or does the engine kind of run on and take 2 or 3 seconds to die? I work on small equipment everyday all day. Want to know what my guess is? remove the hose where it connects to the carb, Make sure the fuel is flowing well here. If it's not flowing well then the engine may be burning the fuel faster than it was get gas to the carb. If the fuel flows slowly try to remove the gas cap and see if it starts flowing faster. My initial guess is the gas cap not venting correctly. So if it's running and it sounds like its going to die, try to quickly unscrew the gas cap and see if it picks back up. If nothing works, write back and let me know.
Phil B4 years ago
The voltages in an ignition coil are too high for a multi-meter to handle without damage. Sometimes you can get a feel for whether the problem is related to the fuel system or the electrical system. If related to the fuel system, the engine may stumble before quitting. If related to the electrical system, it is more likely to just quit suddenly. Check the routing of the coil wiring, especially on the primary side, to see if years of vibration have worn away the insulation from a wire and heat causes it to move so it shorts when the engine is hot. You will likely need to remove the flywheel to check the coil wiring. If the engine is stopping after it heats up, it seems something is moving or changing due to engine heat. What about the gaskets on the carburetor, both between the bowl and the carburetor body, and also the gasket between the carburetor and the engine block. If the engine is a few years old, the gaskets may not seal well or the mounting bolts may be loosened slightly. If the engine is older, the float could have a leak and could have become heavy. If the float is plastic it is porous and will also become heavy after a few years from absorbed gasoline. I would also check the engine compression when hot to make sure it is within acceptable limits (around 80 pounds). Is the engine receiving lubrication. If not, the engine could seize and stop. But, it would not likely start when cold until the piston was made free again. In order to run, an engine needs air, fuel, compression, and an ignition spark. If any one of these is compromised, the engine does not run. I hope something in this helps.
frollard4 years ago
Indeed - it could be the coil misaligned, bent shear pin (make sure its square), 'new spark plug' - did you make sure it's gapped properly for your engine?
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