clean the air filter and spark plug, if it is 2 cycles engine make sure you mix the right ratio (fuel and oil). now use quick start fluid spray in the air in take several time and start the engine. if it is on then you are good, but if it is on for only 2-5 minutes and off. there is only 2 things.
+carburetor is bad. you need to rebuild it by changing the new o-rings, diaphragm & gaskets or even get the new one)
+vacuum might be leak. you need to check the fuel line to see if there are any leak.
if after you use starting fluid and it is not start, there are 2 things happened:
+the piston ring might be cracked. (this case you need to buy the piston ring and rebuild it if you can do it yourself, if not the have the repair shop to do it)
+the electrical distributor or spark plug might be bad (you can check by take out the spark plug and hook it back to the wire try to start to see if there are any lighting b/t the gap of the spark plug). it nothing come out the let change the distributor and spark plug. it should work though.
in sum, there are mostly 3 main things in the small engine that cause the problem: the engine block (piston), the carburetor, and the distributor (included spark plug ).
if spay the start fluid, and it is on and off after awhile : the carburetor is bad
if spay the start fluid, and it is not start: there are 2 things: either distributor& spark plug is bad or the piston& piston ring is bad.