1863 not starting
 

Picked up a nice 1863 couple weeks ago. It started and ran fine. Mowed couple times with it, noticed a loss of power then it would pick back up, like a dirty fuel system/carburetor. Replaced spark plugs, air filter, fuel filter, changed oil and filter. Cleaned out carb bowl, blew out the passages. Ran great. Tried just today and engine decreased in power. Limped back to the garage and took carb off, didn’t appear dirty inside. Put back on and now it will just crank and no start. Has 840 hrs. I just assumed it’s a fuel issue, but just guessing, don’t have any experience with the command engines. Not sure where to go from here, thanks for any help

Did you re-attach the lead for the fuel solenoid ?

Pretty sure that has the shut off valve's on the gas tank. They get plugged up with crud.
Might also be the fuel line failing and not allowing sufficient flow?
I think most guys replace the valve's and the grommets and all the fuel line.

Yes, reattached fuel solenoid wire. I can’t confirm if the fuel lines and shutoff valve are bad or not, but I am getting plenty of fuel. What am not getting now is spark. I cleaned the terminal at the ignition and no change. It would crank and then at another turn of the key do nothing like a bad ground. Also the machine is an 1863 not a 64. Was a one owner with all original receipts, manuals.

I'm pretty sure the fuel solenoid gets power from one source in run and another in start. Verify that the solenoid is getting power in run and start key positions.
Cannon

No spark, you might want to check the coils. I have a Kohler Command 18hp that acted the same and i found intermittent spark using a spark tester between the plug wire and plug. I changed out both coil packs and it fixed it. I contemplated off brand but ended up spending the $100 for OEM Kohler. At least thats what they stated.

I confirmed I’m getting power in start and run. Next I went to coils. Yanked out engine, cleaned it up, waiting on the coils now. The valve grommets disintegrated on both sides of the fuel tank just touching them so replacing both of those and all fuel line. While engine out doing both crank seals. So hopefully once it’s all back together this will solve my issue.

Might as well replace the head gaskets while it is out. If they have not been changed you will be going that next.

Got it up and running. Runs great and smooth. Replaced both ignition coils, fuel tank grommets, valves and fuel line, crankshaft seals, head gaskets and carburetor. Looks and feels like a new machine

Way to get after it!
From your initial post, I would have bet on the fuel lines. When you said no spark, I would have first tried an ignition switch. They are only about $20. Good to have one on hand. I've seen 4 different GTs have the ignition switch go bad in the past couple of years.
Good to see you got it running like new!