All Fouled Up.
I thought I was making some progress with respect to getting the carburetor to properly meter air and fuel. It's doing the job alright (as it always has been) but it's not doing it as efficiently as it should (or as it did from the factory). I continue to deal with the hesitation/surging issue. It's very subtle but when things are right, the motor runs great and pulls well (for 125cc). When it's 'off', it's noticeably down on power. I experienced both scenarios on the ride to work this morning. So, obviously I haven't resolved the issue.
While I was shopping for o-rings, last weekend, at the local (industrial) hardware store (that caters to the trades), I met one of the employees that happened to have some familiarity with the carburetor I had in my hand (the one from the ATC200X). His suggestion, should I fail to make either the OE or ATC carburetors work, was to get a replacement from that large on-line auction site. Apparently those "Chinese knock offs" are pretty good. He's used them on more than one occasion. The issue is that one only seller seems to carry them for the NX. And, while they look correct on the outside, I'm curious what the measurements are, especially the venturi and jet sizes.
I did contact them, previously, regarding a rebuild kit (before I knew the true nature of the problem (although, I'm not quite sure if I really grasp the entire issue). However, they seem to be a little hard to get a hold of lately. They do have a good return policy (30 days) but I would prefer not to pay the shipping, both ways, if I don't have to. The price isn't terrible ($65) but I'm leery of ordering something without a little additional information. Perhaps I can see if they have a non-Toll Free number.