An engine needs three factors present and in the correct proportion to start and run properly - the correct air/fuel ratio (fresh, quality fuel is a must), sufficient compression (arguably 90 P.S.I. or better) and sufficient spark at the correct time. If one of these factors is missing or out of proportion, the engine will run poorly or not start/run at all. Your task is to find the missing factor by inspecting and testing the systems involved. Which factor is missing or out of proportion in your case?
If you do not know how to check for spark or perform the necessary checks and tests, youtube has some videos that will guide you through the process. Simply search youtube for what you want to test or check.
There are conditions that will prevent an engine from starting even though all three factors are correct such as a plugged muffler/exhaust, old/contaminated fuel and I am sure there are more possibilities but I will not try to list them all here so I am going on the assumption that one of the factors is missing and that all other components are functioning properly.
You will need a compression gauge to test compression so if you do not have one or do not have access to one you will need to take it to someone who can test it for you. You will also need a spark checker which can be made from an old, working spark plug by clipping off the side electrode, connecting the plug to the lead and resting the metal hex of the spark plug on the metal part of the engine but this is not always as easy as it seems as many engines have plastic shrouds and other obstacles in the way. My method of testing for lack of fuel is to spray a shot of carburetor cleaner directly into the carburetor (air filter removed) and try to start the engine. If the engine starts and runs for a second or two and then dies you most likely have a fuel delivery problem.
Perform the necessary tests, report back with your findings and you will receive further advice based on your answers.
