A service manual won't really show you much about cleaning a carb, so I thought I would post this:
First, you need to take the carb off. Next, remove the bowl and remove the float and float valve. Now, remove all the jets and clean them and make sure the hole in the jets isn't clogged up. Hold them up to light and make sure you can see through them. If they're clogged up, use a piece of wire from a wire brush, the wire from the inside of a trash bag tie, a small sewing needle, or just anything small enough than you can poke through the jet and remove the clog. Don't use anything big enough to damage or wallow out the holes in the jets. Soaking them in carb clean will help if you have a hard time unclogging them.
Now, turn the pilot screw all the way in while counting the number of turns it takes to turn it in. Remember that number because you will need it to be able to put the pilot screw back to where it was. Just turn it in until it stops. Don't tighten it or you will damage the end of the screw. Now, remove the screw completely. There will be a spring, washer, and tiny o-ring on the screw, so don't lose them. The washer and/or the o-ring will probably stay down in the hole and you will need to dig them out with a tiny screwdriver or pick. While the pilot screw and all the jets are out, blow air through all the passageways in the carb body, especially the ones that the slow jet and pilot screw go in. Don't forget to blow air through the fuel inlet to the carb bowl and out the hole where the float needle goes.
Next, clean the inside of the carb and the carb bowl with carb cleaner and remove any buildup in the bottom of the carb bowl. Get the cleaned pilot screw and put the spring, washer, and tiny o-ring on in that order. The washer goes next to the o-ring, not next to the screw head. Be careful that the o-ring goes into the hole straight and square and put the pilot screw in and tighten it all the way in to the lightly seated position. Remember, don't over tighten or you will damage the end of the screw. Now, back the screw out the same number of turns that you counted when you turned it in earlier. Check the end of the float needle for damage and also check the hole where the needle seats for any damage or dirt buildup. Reinstall all the jets and reinstall the float and float needle and put the bowl back on. Reinstall the carb.
If the carb was real dirty and the passageways were stopped up in the carb body and you couldn't get them unclogged by blowing air through them, then you will need to soak the carb in carb cleaner overnight. You can buy one gallon buckets of carb cleaner from the auto parts store with a basket to hold the carb. Make sure you remove any rubber parts, such as o-rings before spraying carb cleaner or soaking the carb in carb cleaner. The carb cleaner will melt the rubber parts.
Here is a good link to read to familiarize yourself with cleaning carbs. It pertains to motorcycles, but ATV carbs are basically the same. They might look slightly different, but the cleaning procedures are the same.
How to Clean a Motorcycle Carburetor, the RIGHT way. Evan Fell Motorcycle Works