RE: DA 100 Carb problems
Is your choke closed completely?
On several engines following rebuild, I filled the demand regulator chamber, this was accomplished by pressing down the diaphragm with a small allen key through the vent hole while proping. If the pop off pressure is high, the fuel pump cannot over come the pop off. I actually could hear the air vent once the diaphragm was pressed down.
Can you rig your fuel can to the carb to provide positive presure if you suspect a tank issue?
If you been doing this for 20 years you surely know what's right and wrong, thats why I would suggest depressing the diaphragm.