The key may lie in the fact that the car was previously fuel injected.
The Spica injected car requires something like 60psi of fuel pressure
and has a high pressure pump located near the fuel tank/spare tire well
under the car. Carburetted cars only require something like 4-10psi.
60 psi? I could certainly be wrong, but the Spica car's "low fuel pressure"
light goes out between 7 and 9 psi, so 60 psi sounds a little high. I think
the issue is more one of the volume of fuel the pump can move; something
like .6 gallons/minute, enough to fill your little float chambers about 50
times over.