Thanks Norm,
I did figure something out this morning, which may help to diagnose the problem. It seems to be getting too much air. If I put my hand over the end of the tube it starts first time, then if I gradually open my fingers a bit I can get it to idle on "Slow" position. It will still rev up normally if I pull the lever up while holding my hand over the snorkel in this choked manner. I can do the same by squeezing the rubber hose. Sounds funny, but if I clamp the hose until it is nearly closed, it runs fine.
