A happy side-effect of the Pirelli SL26 in the 90/90 size up front is that it almost perfectly compensates for Honda-sans hopelessly optimistic speedometer. Yup, 35 indicated was 34.5 on the GPS. Under 3% error, still on the safe optimistic side.
Tonight I installed the Polini ***-006 belt for Italjet and Derbi Vamos. 668x16.25. I shimmed the front pulley boss 1.25mm and immediately hit a snag. When I started it the noise was immediately apparent: The kickstarter castles were just barely caressing each other. A temporary fix with a couple of washers between case and cover let me go out and test. I'll get and glue on a second gasket.
Oddly, despite riding the very outer rim of the driven pulley, take-offs are not much different. Maybe it needs more shim to drop to center in front? I just happened to have the Perfect Washer for the occasion, but would not be able to find another.
Engine speed through the midrange also about the same. Seems to drop RPM a bit sooner as I approach top speed and may need lighter rollers to get over the top. However peak speed of 53.0 on the GPS was without trying very hard - better than the first-run 52.6 in Build Chronicles. Still running 340 at WOT, up to 375 when I let off.