When you have the low too lean it will want to die when you advance the throttle fast. Keep richening it up till it doesn't plus a tad and that should be about right. I basically just repeated what Ralph had said. Then I ALWAYS reset the high after I touch the low.

Any burbling (4 stoking) is an indication of a very rich condition. I usually set my planes so there is an ever so slight burble (barely detectable) in level flight but it clears when pulling hard in an up-line. Then when winter comes and the 100+ degrees go away I let them run a little leaner.

Oh by the way crash have you look at your plugs, they can tell you a lot too.