It all comes down to the rollers, and belt. The old stuff was worn, and therefore lighter. That makes the rpm's higher, and the bike peppier.
I don't know if this was addressed before here... You will most likely be happier w/ lighter rollers, and the bike will respond better than it ever has.
The next point to consider is the control spring in the rear pulleys. It IS softer than it was new, and it IS allowing the pulleys to open sooner.
Replace both the spring/rollers, and you can fly to the Sun.
