Let me guess: Setting the needle for full throttle is easy. But, when you start throttling down it loads up and dies.
If this is the case and the timing is correct and the valves are adjusted properly, then this is the cure:
Remove carb from engine. While looking at the inlet of the carb rotate the carb barrel with the throttle arm toward the idle position until a tiny opening between the carb housing and the hardened steel throttle barrel remains. Mark the hardened steel throttle barrel at the center of the crescent wth some form of scribing tool and remove it. With a round needle file or similar dremel attachment carefully file/grind off the sharp edge of the crescent at your mark. In essence you're beveling the hole drilled through the throttle barrel.
It doesn't take much to take too much off the edge! Just take off a little bit at a time until your engine transitions properly.
I have drilled out the airbleed hole to 3/32". It didn't work. After making the adjustments to the barrel more than half of the enlarged airbleed hole is now covered by the screw.
The problem was too much vacuum within the carb resulting in too much fuel and not enough air.
BTW, I tried to find the thread where this info was listed but, couldn't find it. I'm not sure where it is now... it's around here somewhere... anyone seen my marbles? I seem to have lost them...
