Could this cause a vacuum leak?

[TOOLS1]

As some of you know, I have been having one helluva fight with Zenith's CB 160 we restored trying to get it run correctly. Now before we get too far in, this bike came to us in the sorriest condition possible. Locked engine, parts, and I mean several parts missing, severe rust, grime, and caked clay. So you might say this was a basket case. After finely sorting out the ignition, I have it running on both cylinders, but the left one that has given me the most trouble is now confirming a vacuum leak. I have replaced the manifold O-rings, manifold, and even tried another carb body. Tonight while loosing sleep over this, it dawned on me that the only part I had used throughout all this testing, was the AIR screw that came in the crappy carb kits. So at 3:00 in the morning, I am out in the shop (one of the hazards of having a home business) removing the AIR screws, checking the O-ring for seal. Seems to be sealing, but then I thought, could the screw be wrong? So I pulled the AIR screws out of another set of dead, corroded carbs, and compared them. They are different, but are they that much different that they would cause a vacuum leak?



I am also wondering if the part where the O-ring goes, might be turned too small keeping the O-ring from sealing on the shaft of the screw? I will have to wait until I can get the old one cleaned up to measure though?
TOOLS

[shinyribs]

1: I have no idea who Zenith is or anything about his bike. ;)

2: You need to get yer azz in the bed.

3: Good catch. I could see that leaking if the I.D. was too small, but that would be the tiniest vacuum leak ever. Sometimes it doesn't take much, though.

[TOOLS1]

I thought I had posted about this bike.


And Zenith

TOOLS

[Re-run]

You know, I have heard a lot of people having trouble with carb kits because parts don't quite match up. It could just be the build up, but the old screw still looks slightly larger. The oring is still on the old screw, so it is hard to judge the spot there, but if it is the same as the rest of the screw, it seems to me that it could easily be leaking slightly.

[TOOLS1]

I think mystery solved, well I hope. Just too measurements of the shank where the O-ring is supposed to seat, and this is what I found. The new air screw from the carb kit. 2.85mm.



Old Honda Air screw. 2.97mm



That makes a difference of .12mm. I am thinking that would be enough to keep the O-ring from seating on the screw.
TOOLS