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24 July 2011 @ 09:04 am
Not My Field  
OK, it's time to play "Who Knows Anything About Small Engines?"

So, the mower here. A few years old, a Toro, i believe. Not kept in the best shape, but more than capable. Been using it every weekend for months. Oil is full, gas is full. Last weekend, pulled it out to mow, it started up, ran for a few minutes then conked out. Starting it up again results in it firing just fine and then dying again almost immediately, and this is repeated until i get annoyed and quit. Gave it a day of rest, tried again, same story: ran for a few minutes, died, each start since is start and die. This weekend, same thing. Replaced the air filter (thought maybe a lack of airflow was the culprit) only to have it do nothing different.

Right. Engines are not my thing. I understand how they work, but know nothing about repair and troubleshooting. Anyone with any knowledge care to take a stab at this?
Blediffe Cannelldariens_haircut on July 24th, 2011 02:16 pm (UTC)
Air filter was my first guess. If you ever run into a mower that keeps speeding up and slowing down by itself, that is probably the air filter.

Spark plug is not my second guess, but it is relatively easy to check compared to other things, and if it turns out to be your culprit, you win. It has probably (statistical likelihood) not been inspected since it was new. Check not only the condition of the gap, but also that of the wire and boot. Unfortunately, if the wire or boot are cracked, that's the whole magneto, since they're all one part.

Since it's probably not the ignition system (that would tend to be more reactive to moisture than to operating temperature, but all bets tend to be off with these things), next guesses lead to the fuel system. You're looking for things like cracking or collapse of old fuel lines, primer bulb, etc. or perhaps a clogged fuel filter. Those things degrade (cracking, hardening, loosening) over time, especially if you don't use stabilizer in your gas, but even if you do.

That's the easy stuff. From there, you're into checking to make sure the shear key which keys the flywheel to the crankshaft hasn't sheared (from hitting a tree root or something) (thus throwing off the ignition timing), rebuilding the carb (similar effects to the fuel line discussion), etc. The aforementioned shear key inspection pretty much means taking the top of the engine apart.

It's hard enough to troubleshoot these things when they're right in front of one.