The vented gas cap has a one way release valve that is pressure activated.
Weed eater gas cap vent.
Inside the cap is a rubber seal which can get lost at a refueling stop causing gas to start leaking.
Rcurren01 rcurren echo srm 225 trimmer you can try with fuel cap off in case the caps vent is plugged not allowing fuel flow and or replace the filer in the tank if you have not already done so still no go if you say primer bulb shows fuel in it and you press the primer bulb say 10x and choke on and still no fuel in engine the carburetor is either not adjusted to allow fuel to enter.
If your motor runs for a few moment and then dies but starts back up this tip may be for you.
Clean the fuel tank and engine with soap water and a rag to help you better determine the source of your leak.
Puncture holes can also come from flying rocks from the cutting head or if you dropped the trimmer against a sharp object.
How to replace the fuel tank vent on an echo trimmer model srm 225 find official echo trimmer parts that fit.
When the pressure reaches a certain point defined by so many pounds per square inch the valve opens by a very small amount relieving some of the pressure.
After removing and replacing the fuel cap the engine again starts and runs normally.
Then stops after another 5.