small engine question

I've got a K532 in a heavy garden tractor.
The engine has started fouling plugs after or during shutdown. When I pull the plugs, they have dry, black, carbon seeming residue on them. Looks like just enough to keep 'em from firing for startup on regular gas.
I can clean 'em with a rag, and give the intake a whiff of ether, and the old chugger will start right up and run fine.
My guess is the things are running too rich at shutdown. Is this the likely case?
If so, should I:
1. go to a hotter plug range
2. go to hi-test gas
3. do something else
If the answer is do something else, what is recommended here? (yes, I know the idea is to find out why it's suddenly running rich on shutdown. It has a new carb, and it's been shutting down and starting and running fine up until several weeks ago. I don't have a clue as to what's changed or what to do with an engine that runs fine. This is where I need help).
I could, of course, just add some TCP or similar octane booster to my regular, if that would solve the problem.
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I dought it happens at shutdown it happens running. Is spark strong and blue or yellow and week. High octane wont help, it is running rich, bad spark or it is burning oil. If it is burning oil a hotter plug and thicker oil. Is air filter clean and choke off.
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Choke is off, and air filter is clean.
The idle run prior to shutoff is a good point. The guy who rebuilt my engine also mentioned doing this. I try to, but not sure I give it enough idle time before killing. I'll try letting it idle longer.
Thanks for these ideas.
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Do you idle the engine down for 15 or 20 seconds before shutting off?
You should do this to prevent raw gas being pumped into the cylinder and not being burned.
Bob
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GO to one of the newer style spark plugs engineered for the new gasolene. They usually start with an LM instead of J8 or D16
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}}} Very good lead. Thanks. {{{
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RB wrote:

It doesn't sound like your plugs are fouling. Are you seeing black smoke out the exhaust? It seems like you have not enough gas or a weak spark. Next time it happens, instead of ether, try plain old gas down the carb.
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Is there a fuel shut off under the fuel tank? If none of these ideas helps, maybe leave the key on, and close the fuel valve when it's time to turn off the mower.
Also check the carb adjustments. Might be running rich ALL the time, and you only notice it on restart. I doubt you'll get a load of carbon on a couple seconds of shutdown time.
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Christopher A. Young
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