This happened to me also. I found that my engines cylinder had too much fuel in it and my heat adjustable ignitor was a little too high. When the engine was flooded and I put the ignitor on to start the engine would continue to turn over but not start check the plug and it was blown- looked like a small ball on the end of the plug.
Make sure your engine is not getting too much gas and your ignitor has enough heat - not too much.
Hope this helps.
Tony
ps - I went through 5 plugs before I figured this out. got the engine running again and adjusted my needle settings.
