Small Engine Troubleshooting Problems? Ask a Mechanic Now.
What is the make and model of the engine? Have you removed spark plug, and with the spark plug grounded, do you have spark when cranking?
OK, do not recognize RST.???
Engine twin or single cylinder? When did mower last run?
Remove both spark plugs and check for spark with plugs grounded. If you have spark, put a teaspoon of fuel into each spark plug hole, re-install the spark plug and see if it will run for a few seconds. If it does, and then dies, we have no fuel through the carburetor.
The carburetor has an electric solenoid in the base of it, it has to click open when key is turned on. Need to see if it is working. Next would be to check fuel supply to the carburetor from the fuel tank,
Here is service manual on the KT725 engine.