Ok man here is what your going to do. To clean my motor I use Carb And Throttle body cleaner feom Advanced Auto Parts. Clean the outside of the motor only with that then spray some WD40 on the one way bearing. Not to much. Now for the inside of the motor.
1) Remove the muffler from the motor.
2) Remove the motor from the car.
3) Remove the exhaust manifold.
4) Remove the carb.
5) Remove the cooling head.
6) Make sure the piston is at BOTTOM DEAD CENTER.
7) Spray liberal amounts of WD40 throught the opening where the carb goes and through all the ports. Let it drain out from the carb opening and repeat several times. I can not tell you it will be 100% clean but it will get most of the gunk out.
If you want to go all out then you can take the entire engine apart and clean everything seperatly with WD40.

Make sure you clean the outside of your motor on a regular basis bcuz dirt build up will hurt it in the long run. It acts as an insulator and your motor can over heat.

Also buy a new pull start and cover up that one way bearing to keep it protected from dirt.

Good Luck.