To the OP:

Couple of questions for you.

1. Is your vent tubing open and no kinks?
2. How far down are you going on idle as far as RPM?
3. Is your butterfly valve closing all the way when you go to idle? It should be open a smidge. at your lowest idle setting.
4. Have you replaced the DLE plug with an NGK or similar?
5 Have you ensured the spark plug boot in firmly seated?
6 ensure the carb spacer block is orientated properly and no cracks?
7. What voltage are you using for ignition?
8. Lastly you might take the back plate off and ensure the diaphragm is intact and not cracked.

Hope this helps

Glenn