DON'T PLUG ANY OF THOSE NIPPLES!!!

The nipple on the casing is to provide the pressure pulse to operate the fuel pump in the carb.

I can't tell with certainty from the pictures you posted, but I believe it gets hooked up as follows:

#1 - connect to main fuel supply
#2 - connect to engine crankcase nipple
#3 - connect as a return line back to the tank (normally the return line from the primer bulb)


If I have them wrong, hopefully someone who has done more conversions than me will help.



<Edit>
I just read your latest post on the SPAD forum... Glad to see you've got it straightened out, but I would recommend running a return line from #3 back to the tank. These carbs will sometimes spit fuel out this nipple. If your saw had a primer bulb, it would be connected here, then the output from the primer bulb goes back to the tank. You CAN eliminate the primer bulb, but it makes the engine easier to start. If the diaphram pump is dry, it won't pump, and the primer bulb draws fuel up to the pump.

Don't forget to leave a vent line from your fuel tank to the outside air, or a vacuum in the tank will prevent fuel draw.