Just wanted to pass along an update. The last thing I did was add that throttle return spring, and I've gone thru a tank of gas where I wasn't messing around with the settings on the Weber.

Pleasantly surprised at the increase in mpg I'm seeing now. Before, with the non-working secondaries on the Mikuni, I was averaging less than 15 mpg. Now, with the Weber, my first tank went almost 20 mpg. That's a significant increase in mpg, not to mention daily driveability, especially with that return spring installed.

Next thing to look into is this rattling sound coming from the carb whenever it's started, and that's whether it's cold or warm. I think it's related to those butterfly plates on the top, and the linkage to them on the side of the carb. From what I can tell, they look to be connected to some kind of "cam" gear looking thing on the side, with an adjustable screw that looks like it's supposed to touch it. Well, in it's current setting, that screw isn't coming anywhere near touching the cam, so I think those butterfly plates are pretty much wide open at start up.

I can live with the rattling noise at startup for now, since it goes away within a couple of minutes. But when I'm feeling frosty, maybe I'll remove the air cleaner so I can see those plates, fire it up, see where the noise is coming from, and figure out what to do next.

But I'm really liking how it runs now, and 20 mpg is an added plus!