Well, if you leave in low rpms can you open up the choke (i.e., remove it) and will the engine continue to run alright?

If you slowly increase RPM's in neutral, what happens; and, it you put it in gear at low rpms does it stall?

The it could be gum, it could be crude out of the tank or fuel line, or other "dirt".

It's possible that your carb is just cruded-up (but I wouldn't assume that first). Do you use an additive in the fuel tank?