Danny,
Remember all the black sediment we found in number one carb bowl?
Sediment will trump the float tang dimple for overflow cause, I think.
Cheers,
The black debris in the float bowl may have also come from a deteriorating rubber disc in the petcock, given the reports of overflowing even after being turned off?
Danny, when going down the road, the float needle is partially open, just enough to match the fuel being drawn by the motor. If something happens to find it's way into that small gap, whether from the tank, petcock, or fuel line, it gets pinched into place between the needle and it's seat as the float rises. If the bowl is drained, the float and needle will drop, and incoming fuel may flush the now free bit of debris to fall to the bottom of the bowl, allowing normal float/needle operation. If the debris is coming from the petcock, turning it off and on may dislodge more material each time, repeating the cycle. Does the petcock indeed leak in the off position with the fuel line removed?