Wow, an ancient thread here.
verify your float valve viton tips are in good shape, clean and closely inspect that no telltale circular wear marks are present, if so, an automatic replacement is called for. Of course, check working fuel levels using the clear tube method. In doing so...let them sit awhile and see if the levels slowly rise.
The fuel "mix" screws should be responsive on an idling EX....turning one in should cause a stumble on that cylinder. If not responsive, there is unmetered fuel getting in somewhere. Check each and you may narrow down whether both or one cylinder is your bad guy.
As posted earlier in this thread...a defective petcock vacuum diaphragm allowing fuel into the carb vac inlet should also be checked and eliminated. Its an oddball, but you never know.
You don't have jet kit or hogged out pilot jets, do you?
If you are so inclined, PM me for further off-forum discussion.