I would lean the low end mixture, that will increase the idle, then just trim it back down.

Did you go through the instructions as to setting the low end???.

It is in the manual under "Adjust the Carburator low-end for idle and transition"


If that is not in your manual you can get it from http://www.bmeengine.com/BMEdocs/BME_Instructions.pdf

All these engines work pretty much the same, it doesn't matter which brand.

The plug gap is not what will give you good transition, read the tuning section and you will get a better understanding.