I had the same problem starting a Ryobi strimmer.Turned out to be a defective spark plug cap. Would start if you applied pressure on the top of the cap but immediately cut out when I removed my hand. I replaced the cap and it now starts and runs fine.
Paul
May 2009
These small two strokes really need their own starting technique.....
Press the primer bulb a few times (If it has one)
Put the choke on full
Apply full throttle
Pull the recoil starter very briskly until the engine pops
Take the choke off, but keep full throttle
Pull the starter briskly again and you're away!