Small Engines (Lawn Mowers, etc.): Weed wacker dies after a few seconds, plastic gas tank, weed wacker

Question
I have a weed whacker that dies off after a few seconds of running..  I've already cleaned the carburetor (both sides) with shop air and made sure that the exhaust screen is cleaned but have not had much success.  My fried has the same problem with his weed whacker.  I have straight shaft MSR211 Echo weed wacker and the carburator only has one adjustment screw, which I have not messed with.  I've noticed that the plastic gas tank has a large crack and am wondering if this leak has something to do with it.  Does the tank have to be sealed, pressurized or vacuum.

Answer
Miguel
The tank needs to be sealed as the carb sucks gas out of the tank and then it gets replaced with air so not to cause a stoppage Check to see what the compression is it should be around 100-120 psi. You need to get a compression tester. Hook up the tester and then pull the starter a few times and see what the tester says as far as psi