The jets arrived, so I sawed off that air restrictor and put #140 main jet in. All I can say is oh my god. Top speed went from 65 on a serious downhill to 78 on a gentle downhill. I feel like it should be running rich since I haven't put the K&N in, but I didn't feel the "jerking" he describes for being too rich.
Here's something though, I guess some GZs don't have an adjustable jet needle!
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So I guess what I have to do is buy a couple washers to emulate a 5th position. I'll pick up a bunch in case I ever mess with the exhaust.