Is it compression relief or something else - 28D7070123-01 11.5HP

[Mower King]

I checked the valve clearances and they're good per the manual. Anything else I should check?

Check your battery, I mean really check it, with an ohm meter as you engage your starter and read that #, what is that #?
If battery tests good, check flywheel key, if it sheared, it moves the Ignition timing and it can "kick back" when you try to start it, kinda like you are describing....but 1st, BATTERY!

 

[bertsmobile1]

Grab a pair of jumpers and jump the starter directly from your car.
Spins normally = starter OK
Now jump directly from the mower battery
Spins normally = mower battery good
Jump with only + lead
Spins normally = ground connection/ cables good
Move jumper to the starter side of solenoid
Spins normally = starter cable is good
Move jumper to battery side of solenoid
Spins normally = solenoid & battery cable is good

 

[MowSlow]

with an ohm meter ...If battery tests good, check flywheel key,

An ohm meter or a voltage meter? And how do I check the flywheel key? Do I need to remove the flywheel for that?

 

[MowSlow]

can you spin the top of the valve in the seat? place your thumb in the middle of them and try to spin them back and forth.

I can spin them but only when they're open (the exhaust valve is a little tougher). Is that the way it's supposed to be?

 

[Mower King]

An ohm meter or a voltage meter? And how do I check the flywheel key? Do I need to remove the flywheel for that?

I use an OHM meter set to 12DC.
To see the flywheel key completely, yes, remove the flywheel...but 1st...check that battery volts under a load of the starter....like I explained earlier!

 

[Scrubcadet10]

An ohm meter or a voltage meter? And how do I check the flywheel key? Do I need to remove the flywheel for that?

voltage meter is good enough, set it to DC volts, 20v. you may need a helper, check the voltage with everything off, key off. then have someone hold the leads to the battery posts while you try to start it, if it drops down to about 10.5 or lower volts, most likely the battery is toast.
this is similar what i use,

 

[Mower King]

voltage meter is good enough, set it to DC volts, 20v. you may need a helper, check the voltage with everything off, key off. then have someone hold the leads to the battery posts while you try to start it, if it drops down to about 10.5 or lower volts, most likely the battery is toast.
this is similar what i use, View attachment 54008

2 wires with alligator clips on the ends = 1 man testing operation.

 

[Scrubcadet10]

I bought a set of those alligator clips.... Have no idea where they ended up though

 

[MowSlow]

if it drops down to about 10.5 or lower volts, most likely the battery is toast.

It meaures 12.7v with the key off then drops down to ~9.8v when I try to start it. But it still spins better than it did before - probably because I have the carb. and valve cover off. I guess I need to buy a new battery

 

[bertsmobile1]

I can spin them but only when they're open (the exhaust valve is a little tougher). Is that the way it's supposed to be?

yes