I found the vapor pressure of methanol at 80 degrees F. It is only 2.5 psi. Since atomopheric pressure is about 15 psi. it means that the carb. would have to be drawing down the fuel pressure by 12.5 psi, which is impossible. I estimate that a carb. can pull fuel up at most 12" which equals a suction of less than 1 psi. So it would seem that the bubbles are definitely not being caused by the methanol vaporizing.

Since engines get hot, I checked the vapor pressure at 100 degrees F and it is still only 4.63 psi, still far too low to cause methanol to vaporize. At a pressure drop of 1 psi, it would take a temperature of approx. 140 degrees to cause vapor bubbles.