First off take the engine out of the car. Then you can take the carburetor off and spray it with nitro engine cleaner. Also spray down the whole engine. It will remove all the oil and dirt. Use Traxxas nitro cleaner or similar made for rc car engines.

If you want a real good clean you can take the engine head off and spray the piston and sleeve and the engine head. Use a rag to remove the access engine cleaner.

Don't forget to clean off the air filter while the engine is out. Just spray it with the engine cleaner or soak it in soap water. This does a very simple cleaning Job.

If you wanted you could take all the needles apart from the carb and clean them up but that is a little more difficult and is not completely necessary all the time.

Make sure you check for engine damage why you got it open to see if any thing needs to be replaced.

Its that easy to give your engine a good cleaning!