Traction Control Needed...

With a mechanical fuel pump,
There should be a coarse 'sock' filter on the fuel pickup in the tank.
A standard factory type fuel filter after the pump on the line going to the carb.
+ The outlet must be higher than the inlet.
Any porosity in the suction line to the pump and it won't pull as much fuel as it ought.
That could be cracked rubber connector lines or a pin hole in the steel line.

Interesting that it shot lean so quickly. I've gone done the track with the pressure dropping from 3-4 psi to zero but there was enough fuel to make to the line. We thought it was the pump but it turned out to be the feed line.
Vapor lock would/will occur if a portion of the line gets heat soaked. Hard to see how that would happen during the run and not other times but its possible. Has only happened to me when there's still winter fuel in the tank, and the weather is hot. Make sure your lines are away from heat and or insulated. If there's any pre-June fuel in the tank - get rid of it.
This all assuming the AFR gage is telling you fuel in the bowl ran very low.