I assume it's puffing white exhaust smoke. Does it do it on both tanks? Do the fuel lines appear rusty? Have you traced all of your fuel lines for obvious perforations, deteriorated rubber, loose clamps, fittings, etc? When you replaced the pump, did you reset the timing? Are you measuring consistent voltage to the fuel solenoid? How about the advance solenoid? Are the glow plugs cycling correctly? Have you checked them with an ohmmeter?
To check for air entering the system, pick up a 3/8" clear plastic line about 12" long and fit it into the fuel supply line before the filters. Run the engine. If bubbles pass through the line while the engine is running, work your way back toward the tanks until the bubbles disappear. Air will be leaking into the system between the location of the "clear line" and the preceding test location that showed bubbles. You might also try plumbing the 'fuel jug' up to the supply line at the selector valve, bypassing all of the plumbing rearward to the tanks, to see if the problem clears up.
1
