John Deer L110 with Kohler 17.5hp backfires wont start

The twin cylinder engine has two ignition modules with kill wires that connect to the ignition switch M (magneto) pole. When the switch is in the off position the kill circuit connects to battery negative. The safety circuit effects a similar connection to battery negative.

Mice like to nest under the engine fan shroud and chew everything. Regardless, you need to remove the engine fan shroud for inspection and clear out the inevitable mouse house as the engine will overheat and damage the heads if the nest material is not removed completely.

See attached wiring diagram for reference.

look down inside air cleaner before starting next time , if theres more than a finger full of motor oil in there then your head gaskets are going

this could be a engine timing problem this model should have a 17.5 hp kohler engine , now kohler's are now famous for having coil problems cus of overheating it and the other cause could be if you reciently shocked this engine hard (Heavy load) sometimes the flywheel pully (iron thing on top) comes loose or you shear the keyway on shaft anyways ck out my youtube video on easy way to change kohler coil for help doing this (all you need is 6 mm wrench , two hands and a playing card)

given the info available , it sounds like either a hole in the piston or a burnt/stuck valve. the popping sound could be a backfire, from improper detonation of fuel ,a simple compression test will tell if this is in fact the problem.

what color of spark, might have a bad spark plug, your plug might not be hitting hard enough

my 15 hp kohler engine backfired while i was using it, now it wont crank and backfires thru carb

The woodruff / flywheel key is likely partially sheared. Pull off the air housing, remove the starting clutch, to get to where you can see the flywheel key. I bet you will find that the key has distorted. Easily replaced once flywheel is pulled. Make sure to use the correct key when replacing it.

CK THE FLYWHELL KEY

1989 Kohler 20 backfires through the exhaust. What are the possible causes?

Try changing the spark plug.