First, you must not "relieve the throttle" until the machine has warmed up - probably for at least a minute on zero choke. Open the choke to the partial position after its initial burp-and-stall. Then start it, and open the choke the rest of the way ASAP. If you do it too soon, it will stop. If you do it too late, it will smoke, spew fuel out the exhaust, stall, and be hard to start again. At this point it is possible that the fuel "leak" you have might be just over-fuelling, resulting in raw fuel coming out of the muffler and the engine rich-loading and stalling.
These things are not easy to use, it takes practice to make them run at all and then they are still pretty ordinary compared with the worst 4 stroke lawnmower you will ever see. There is a reason that so many contractors use the Honda 4 stroke trimmers: they may be heavy, and expensive, but they are very easy to start, and you can let them idle without them fouling the spark plug.
