I've just rebuilt my first pair of Weber IDF carbs and it was quite an adventure. I probably could have bought a new pair after all the replacement bits I needed to hunt down and buy. Anyway, they're done except for the starter circuit, which I realize isn't part of the normal build.

My question is about blocking off the circuit. I've read on the Samba and 356 registry about procedures to drill and tap the holes for the starter valves and jets, but the best articles have dead links and no photos.

All I'm trying to find is if I even need to bother. None of the holes for the valves are jets are threaded. The bottoms of each tube seems like they were never machined for the circuit to begin with. Perhaps cast but not machined. I know that some, but not all, Webers need the modification for drilled, tapped, and screwed holes. Do my carbs need this procedure?

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If they did not have the brass plunger and spring assembly in the holes, then they were probably not tapped from the factory. I have one pair that is like this and two pairs that the starter circuit is open.

If you are sure that the circuit is closed, no need to drill and tap them. No gas will ever enter that area behind the backing plate.

Unless your absolutely certain the circuit is closed you'll need those plungers in place.

If I remember correctly, you should be able to test to see if they are open/patent by pouring solvent in the vent holes that are connected to the starter circuit. If any solvent makes it's way into the starter circuit behind the backing plate, you'll know they are open and would of course, need to be plugged with the plungers and screws.