Oops, sorry I didn't reply. I was swamped with stuff for my BIL when I read it and never remembered to get back to you.
Sounds like you need to adjust the choke properly (it's opening too soon) and I'm also wondering if the accelerator pump needs seal replacements. Falling on it's face with light throttle usually means the butterflies have opened but the fuel isn't keeping up. bad seals do that since it won't pump a good shot of fuel unless you mash it.