Small Engines (Lawn Mowers, etc.): honda gx120 no start, combustion chamber, fuel mixture

Question
I just bought a aerator from hd tool rental.  Started first pull at store, brought home started first pull used on frt yard.  turned off, changed oil,took off pull cord assm., tightened chain.  3hrs later wont start. seems to have spark with pull cord assm off and turning by hand.  4hp honda gx120

Answer
Jeff

Common Causes:

Check for water in the fuel tank, hoses and fuel bowl on the carb. If water is found, be sure to check your fuel can as well!
Check for a major air leak from around the intake or carb mounting area. If the carb is equipped with a built in primer bulb, check it closely for any major air leakage.
If this problem occurs only during cold starts, you may also have a situation where the choke or primer is not working properly.
Finally, don't forget to check the fuel cap to make sure it's venting properly. A cap that doesn't vent properly, will not allow fuel to flow from the tank to the carb.

The reasons for a won't start problem can be caused by a wide variety of individual or combinations of concurrent problems and the best place to begin is to do a quick check of the engine:

Is the tank full of fresh gasoline?
Does the air filter need to be cleaned or replaced?
Check the condition of the spark plug.
Is the fuel valve turned on?
Is the On/Off switch turned ON?
Is the choke in the correct position or the primer functioning?
Check the oil for correct fill level and quality. *(see note below)

If the problem isn't located or resolved during the quick check procedure, you'll need to check for the following problems:

No ignition spark
Improper timing
Fuel mixture not reaching the combustion chamber
Abnormally low compression
Engine not turning fast enough to start

Suggested troubleshooting order: FUEL - IGNITION - TIMING - COMPRESSION


*Note:
The oil level should not be a factor unless the engine is equipped with a low oil shutoff system, but should always be checked prior to use.