The driver today heard a "pop-pop-BANG". the engine will no longer fire. after some troubleshooting I assume it is a fuel delivery problem. I would need some basic info on how to troubleshoot between the LP tank and the fuel/air mixer.

here is what I have so far:
motor turns
New plugs/Wires
New distributor/rotor
Ignition provides spark to each plug
new IMPCO diaphragm
compression:
-cylinder 1) 70psi
-cylinder 2) 125psi
-cylinder 3) 142psi
-cylinder 4) 90psi
-fuses good

now going to attempt to figure out the following fuel system:
LPG cylinder
adaptor through chassis
12V fuel light switch?
(regulator?) with vacuum line
into (vaporizer?) with coolant hoses
into 12v shut off switch
into mixer-throttle body (vacuum line)

I took the main fuel line off just before the shutoff switch and turned over the engine with no fuel present.