This is one of most common questions - "should I tear into the engine". The honda 4's are one of the most reliable engines on the planet. 22k on a honda motor is nothing. To answer your question - do a compression test of the engine, if that checks out ok - leave the engine alone!!!!
If the engine has been setting for a while - you may want to dump a few cc's of marvel mystery oil in each spark plug hole, let it set for a night and crank the engine over (with the plugs removed) a few strokes to lub the rings up a little.
Get yourself a good shop manual and do a proper tune-up and ride with the wind. If your going to rebuild your carbs - don't cheap out with a rebuild kit - use a honda NOS stock kit - Don't buy a cheapo kit off ebay. In most cases, all you will need to change are the rubber parts. The stock metal parts should be fine to re-use unless your carbs are real junk.
Hackasaw has a good point - if the engine sounds a way off and it's not a matter of tuning, then it would be far cheaper to replace the engine then doing a rebuild. I owned a 72 500 and that little engine was pretty much bullet proof. As a demo for my friends, I use to balance a nickel coin on the engine block and throttle it up to 6 Grand and hold it without the nickel falling over.
One point I'd like to add - under the oil pan is an oil screen filter - you may want to pull the oil pan and clean that screen. If you see tons of metal in the screen - than you may want to question the engine. All and all - your engine should be fine.