Help with balky riding lawn mower

June 8, 2014 4:57 PM

I have a Craftsman riding lawn mower with a Briggs and Stratton 10 HP Model # 214907 engine. I just had it serviced this spring, cleaned the carburetor, new air filter and spark plug, etc. It runs like new when I start mowing, but it dies anywhere from 15 - 45 minutes later, and won't start again until it cools down. Google research is pointing to a bad ignition coil. Is there anything else I should check given those symptoms, before ordering a new coil?
posted by COD to Home & Garden (3 answers total)

I'm better with 2-stroke chainsaw engines than 4-stroke riding mowers, but you can check the coil rather than just guessing, and i can think of a couple other possible causes.

To check the coil, bring a spark plug wrench with you while mowing. When it dies and won't restart, remove the spark plug, insert the plug into the boot on the plug wire and ground the end of the plug against the engine block. Try to do this with the mower positioned such that the plug is in shadow rather than direct sun -- a visored hat might help, too. With the plug attached to the wire from the coil and grounded against the engine block, turn the engine over using the starter button just as you would if actually starting the engine. If you can see healthy sparks jumping the plug gap with every revolution then the coil isn't the problem.

Another thing to try is to open and re-close the gas cap after the engine dies, and see if that makes it possible to restart it. Sometimes the vent built into the cap doesn't work properly, and a vacuum builds in the tank as fuel is used and not replaced by air, eventually preventing gas from going into the carburetor. This isn't really temperature-related but might seem as if it were. When this problem occurs then waiting fixes it because air slowly leaks into the tank, not because anything is cooling off.

I'm also tempted to suggest vapor lock, where some part of the fuel line or carburetor is out of position or a heat shield is missing or something, such that part of the fuel system gets hotter than it should and vaporizes the fuel where it should still be liquid, preventing proper fuel delivery. But I would expect vapor lock to make re-starting difficult after intentional shut-down; I wouldn't expect it to cause the engine to die spontaneously during use.
posted by jon1270 at 5:20 PM on June 8, 2014

I had a similar problem with a 5 hp briggs on my rototiller.

The carburetor was loose where it bolted onto the engine. Like really loose. Im surprise d it ran a t all.
posted by bricksNmortar at 7:09 PM on June 8, 2014

Check the mower's manual for the correct plug type, and make sure that is what was installed, and then in addition to checking the spark (as jon1270 mentions), check the gap of the plug as well. A $4 plug is a lot cheaper than a new coil, and pretty easy to install.

(Vapor lock is a good second choice, as could be carb problems - tacky bowl, did they goof around with the needles at service time, etc. I assume someone else serviced it, and while I love my local Ace, they've done me wrong in giving me an incorrect plug twice when I was doing the work. So I pull the manual out and double check the equivalencies, since B&S always says OEM, but you can find Champion equivalents etc)
posted by k5.user at 8:54 AM on June 9, 2014