Sunflyer-

This information maybe too late to help you but I found out something about this carb that I think has been missed. Specifically, the U-shape yoke that is bolted to the idle mixture control valve can be attached too different ways. One way and the engine barely runs, flip it over and the engine will run fine. I had the same trouble you did, and even cleaned out the carb. After reassembly, it ran no better. I took the carb off and looked at it from the bottom. I discovered that the slot in the spray bar was only seen when the carb barrel was wide open, but vanished before the barrel was 20% closed. At first I thought the carb was manufactured wrong. That's when I took off the yoke and noticed that the connecting slot is not symmetrical with the yoke. I flipped the yoke over, reconnected it, and now the engine runs perfectly. Hopefully, you can use this information. If not, there maybe others that this information will help.

Don Myer, Kalamazoo, MI