Troubleshoot a Small Engine Problem

Got a small engine that does not want to run? Before you spend lots of money at a mechanic, see if you can find out the problem for yourself.

Steps

Check the fuel supply. No gas, or old gas, is frequently the only problem, especially when starting a small engine at the beginning of its season. An engine needs clean fresh fuel. This fuel needs to be free from water and debris.
Check the air filter. If the engine can't breathe, it can't run! The filter should be relatively clean. If a purple air filter has turned brown or black, it's probably time to change it.
Many engines that will not crank or run well need a spark plug. This can be purchased at the local hardware store along with a wrench. Just ask!
If new spark plugs or a new filter doesn't fix your engine, crank it over a few times (or run it for the short time it will run), and then pull your spark plugs and look at them. A black or sooty plug indicates the cylinder it is running too rich (leaking fuel injector or plug not firing well). A white and ash-covered plug can indicate the cylinder is running too hot (sticking fuel injector, wrong spark plug). If the plug does not "look normal", but you are unsure what it means, take the plug into a shop and ask! They should be happy to help.

To prevent fuel problems from developing, always "winterize" your small engines prior to long-term storage. This involves draining fuel, among other things, and allows a fresh start in the spring.
If the small engine in question is used infrequently or seasonally, it is a good idea to use a fuel stabilizer product every time you fill the engine (or your gas can) with fuel. This substantially lengthens the life of the fuel.
Don't be afraid to ask as many questions as possible to answer your questions. A repairman will not just divulge advice considering he gets paid for what he knows. Would you tell some kid in a greasy shirt how to set up a wireless internet connection knowing you could make hundreds connecting it up for him or her?

Always thread a spark plug by hand and tighten no more than one and a half turns with a wrench; if you strip the threads by tightening too much, this can easily destroy the engine.
Always remove and replace spark plugs after the engine has cooled. Some engines use aluminum threading for the spark plug sockets, which is easily destroyed if force is applied when hot.

If after installing new plugs, you hear a consistent clicking noise, the spark plug is loose, give it another half turn and restart the engine. Noise should be gone. never turn the plug over two half (one whole) turns after hand tightening. You will destroy the engine.