There is nothing more frustrating than getting ready to use your small engine powered equipment and discovering it won't start.  With over 12 years of experience in dealing with small engines, I have developed a systematic approach to troubleshooting a "NO START" condition.  It works for me and I hope it will help you out as well!

       THE COMMON SENSE BASICS
      
       A small engine, as well as any other internal combustion engine, has to have the following in order to run:
      
       Fuel & air mixture
       Fire (ignition source, a spark from the plug)
       Compression
       And these things have to happen at the proper time (Timing)
      
       Without one of the above the engine will not start let alone run.
      
       We'll start with fire
      
       CHECK THE SPARK PLUG
      
       Remove the plug to check for fouling either from fuel or oil or to see if the electrode has been burned. The air gap should be checked at this time also with a feeler gauge. The most common air gap is about .030 in. If you are unsure of the plugs condition, go ahead and replace it.
       To check the spark plug wire, you will need an inexpensive tester that can be purchased from any auto parts store. One end of the checker is hooked to the spark plug wire and the other is fastened to a suitable ground. (Away from the carburetor!) Pull the starter rope or turn the ignition key to start and watch the tester. There should be a blue/white spark present. A reddish tint or no spark indicates a problem with the coil, the flywheel surface, or a possible sheared flywheel key. You can tackle these problems with the help of a repair manual or consult a repair technician.
      
       FUEL & AIR
      
       This may sound crazy, but did you put gas in the tank?! I have had many people bring me a piece of equipment that would not start only to discover they had not put fuel in the tank. (We all have our moments). Make sure the fuel you use is fresh. Old gas can create many problems in the carburetor that will cause poor or no running situations.  Check the air cleaner filter. Is it a paper or oiled foam type and is it clean? This is where the air portion comes in. A clog filter will reduce power, use more fuel and eventually cause a no start. If it's paper, replace it! If it is an oil foam filter and is not deteriorating, it can be washed in a dish detergent and water, (NO GAS!) solution. Rinse well, pat dry and re-oil with about a tablespoon or so of fresh motor oil. Check or replace the in-line fuel filter, if equipped.
      
       Adjusting the carburetor mixture screw can sometimes correct a no start. This screw is located on the carburetor close to where the carburetor attaches to the engine. (Usually, this just a rule of thumb)  Most carburetors only have one adjustable mixture screw. It is referred to as the idle mixture. The high speed mixture is controlled by a fixed orifice in the carburetor. If a high speed screw is used, it will usually be located on the carburetor bowl.
       To adjust, gently turn the screw clockwise until it seats or stops. DO NOT TURN IT TIGHT or damage to the needle end will result.  Back the screw out 1-1 1/2 turns and start the engine and allow it to warm up. At idle, turn the screw counterclockwise until the engine starts to run rough, turn it back clockwise until it begins to run rough again, then turn back counterclockwise to the mid point between the two. Do the same for the high speed screw, if equipped, only move the throttle to fast before beginning this process of adjusting. Check all fuel lines and fuel tank for obstructions.
      
       COMPRESSION & TIMING
      
       These two can be checked with the proper equipment, but should be left to a repair technician. One thing that you can check is to see if the flywheel key has been sheared. This key is located between the flywheel and crankshaft and is responsible for the timing of the firing sequence. To check, remove the blower or top cover from the engine. Look for the groove in the crankshaft and flywheel. The key should be seated in this groove with no offset. If it is sheared, the grooves will not be lined up. Replacement can be made with the aid of special tools and a repair manual or consulting a repair technician.
      
       I hope this article has given you a little help in correcting a small engine problem. While this was written mainly for 4-cycle engines, some of the techniques can be applied to 2-cycle engines as well. I hope to provide an article on 2-cycle engines in the future.