Yep, the screw is just the speed screw. I too had to find the "sweet spot" on the choke for best starting and it varied between the two bikes. So did the mixture (clip position).

I finally tapered the needle on both bikes so I had optimum mixture. One position on the needle was a bit too rich, the next one was a bit too lean. Tapering the needle with a cordless and some 320 wet-or-dry sandpaper made 'em both just right.

* Do not attemp tapering the needle unless you are adventurous and have a little patients and time. You'll have to "adjust" the taper a tiny bit, re-assemble, test run, dis-assemble, repeat until it's right.

Well worth the hassle.