R Break, Hopefully you are still around. I just finished a 581 Vinson for a friend of mine and have about 6 hours on it. All in all it is running pretty good but it is a little weak out of the hole. This has a lot to do with clutching, but it is fairly limited to what you can do with that on the vinson. 28" mud rubber doesn't help. I don't have a afr meter but have a pretty good feel for jetting. I am running a pretty long duration cam with this set up so I probably should go up on the pilot but the stock 35 at 2.5 turns is a little rich if anything. Running a 155 Keihin main and have lifted the stock needle using 2 shims (sorry, didn't measure them). Running at 3300 ft. I was wondering if you did anything with the brass vacuum air jet to lift the slide quicker. I am reluctant to start cutting the spring as it is pretty light already. I would greatly appreciate it if you would share anything else that you may have found out with me. Hopefully I'm not doomed on the bottom end with the long duration cam, 11.5:1 should help compensate for it though.