I just installed a new honda gcv190 on my old snapper push mower, and it won't start. I put in the oil, put in the gas, the spark plug is installed correctly
CTM
Generally, it usually a lack of spark or fuel that would prevent an engine from starting.
To check spark, remove the spark plug, but leave it connected to the cap. Grip the rubber cap, and press the tip (electrode) of the spark plug against a metal part of the engine block. Have a helper pull the starter grip, and examine the gap between the electrode and the tip of the spark plug. You should see a light spark jump the gap. If not, the on/off switch may be in the wrong position or not wired right. Re-check after inspecting the switch and wiring. When/if you get a good spark, move on to fuel troubleshooting.
Confirm the choke is working, regardless of the engine's temp. Make sure the choke plate is fully closed when the choke is engaged. A partially closed choke is not enough to get the engine to start.
Next, confirm there is fuel reaching the carb by loosening the drain bolt on the carb bowl. If no fuel is present, check the fuel supply, fuel valve, and tubes.
If fuel and spark are present, then it's likely to be a blockage or some debris in the carburetor. Disassemble and clean, reinstall with new gaskets. A detailed procedure is in the Sticky section at the top of the Honda Forums area.