choking hazard

[fordsparky]

 

I replaced my coils, plugs, wires, oil, air filter, and finally having my carbs properly tuned...the machine starts and runs great - even after sitting idle for a week. Only 1 problem left...as long as I start bike without choke (or at least only for 2 seconds) all is good, but if I choke for over 20 seconds it will foul #2 plug. Bike info - 1979 CB750 limited stock except for 4 into 1 exhaust. All ideas are welcome, thanks.

[Re-run]

It is mostly likely that the idle jet may be slightly dirty. I would initially try to run half a can of seafoam through the tank, that alone might clear it up.