Wow, I can't respond to all of the comments posted in response to your enquiry, but you definitely don't need to "buy a new one."
A new spark plug is so inexpensive, it can't hurt to try that. I would add that you should try to purchase the exact brand of spark plug that came with the unit originally. If it's a champion, buy a champion.
I wouldn't have high expectations though. With today's gas containing so much ethanol, my guess is that your carbs need a cleaning. Even with all of your preventative maintenance your carbs will still get "gummed up" unless you are using up the gas within 2 weeks of buying it.
Look for a local small engine repair person. Not a major dealer. Look in the yellow pages under small engine repair and find someone off the main drag, likely in a subdivision.
Describe your issues and leave the unit. I paid $65 and that included a carb rebuild, oil change, air filter, sharpen the blades. When I picked up the mower, the nice man who fixed it brought me back into his shop, ( in the garage of his half a million dollar home) and showed me the bottle of fuel stabilizer. He said "use it in every tank all the time and you'll never be back." And by the way, he said my kids could inherit the TORO if I wanted them to. He wasn't doing all of this for the money, he really liked keeping stuff out of the landfill and promoting looking after your equipment.
If you can't find a local friendly neighbourhood small engine mechanic, you can also try a product called "Mechanic in a Bottle". Exactly as I have spelled it. It is very hard to find, but it cleans carburetors and reconditions the soft parts at the same time. You can google it and read about it. If you can't find it, PM me and I'll mail you a bottle for the cost of it. Around $8 I think. One bottle can treat 4 engines I think.
The point is, find someone who is really interested in small engine repair and you'll have someone in your corner, that's for sure.
That HONDA mower you have is worth a lot more than you think.
Sincerely,
Walleye72