I've heard alot of "left turn" complaints...What I have found is most were not considering what else your doing when you turn left, which is getting back in the throttle after being completely out of it.
When I built my own carbs I always had that problem. I could not "jump" back into the throttle, had to roll into it.
When I went started buying carbs, and using external fuel pump, no more problem.
With the EC Carb..it didn't care how or when or what I asked from it, it gave it to me.
It is not A firing issue IMHO. It is fuel related. I am not a Carb expert at all....actually, I quite suck at it, but I know when the carb is the problem and I believe that is what you guys have.
I don't buy the "turn the carb around" trick - but Lester has built alot more engines than I have and had alot more success. But to me, the bowl should be full when your getting back in the throttle and orientation wouldn't do a thing with a full bowl.
When you jump in the throttle, the carb gets a sudden and massive flow of air, if it cannot feed the fuel to keep up with the air it will cut out..which is often confused with a bog. If it gets too much fuel it will bog, then clear out and run. Either way, that sudden on the throttle hesitation is a fuel issue, and fuel issues are in the carb.