Modern Vespa

This isn't exactly a Vespa question, but the principles are the same and there are plenty of experts on this forum to ask. At 12,000 miles I replaced the belt in my Yamaha Zuma 125. At the same time I replaced the original rollers with Dr. Pulley sliders, same weight (12 grams). I had no complaints about acceleration and I wasn't looking for any drastic improvement in performance. I thought the Dr. Pulleys might add a bit to the top end speed, and may wear longer than the original round rollers.

Now, the Zuma accelerates off the line to 20 mph in about the same way it did before, though maybe a little quieter. Then, from 30 to 40 mph it's revving a lot more. At 40, it shifts up to "high gear" and everything's fine again. But I think it should start shifting up sooner -- not so much rev and more go, so to speak.

Am I correct in thinking that adding another gram or two to the weights will cause the variator to start shifting to a higher gear ratio sooner, like about 30 mph instead of 40? Thanks for replies!

You should post this on a Zuma forum where you can get answers from Zuma owners who have made these changes.

The heavier weights will cause your belt to travel to the outer pulley later, not sooner. On a 125, I like sliders that are one gram lighter than stock rollers. If you want more punch off the line and better low and mid range pull, you can also change your clutch springs to a higher rpm.

Yeah, heavier weights will make it "shift" slower, but it will be less "revvy." If you do try it, I suggest a smaller increment than 2 gs, a little bit goes a long way.

the original weight rollers does not make the same for sliders as they have different characteristics. drop down the slider weight to 10gr.

The "off the line" performance is in the clutch.

At high speeds the variator is maxed out (even with light rollers) so it's mostly like a fixed gearing.

The range in the middle is down to the variator.
If the RPMs are too high, install heavier rollers
If the RPMs are too low, install lighter rollers

Key is a good tach and knowing what RPM the engine produces max power (that is your target)

This is what I was looking for. I don't have a tach (yet) but my ear tells me it's revving too high around 30-40 mph. It acts like the engine is revving a lot and not pulling as much as it could.

Any suggestions for an add-on tach?

there are many but these have been used with good results

http://www.trailtech.net/tto-tach-hour-meter-black-5333
https://tinytach.com/gasoline.php
https://www.amazon.com/Shindy-17-863-Digital-Tachometer/dp/B000GUUULS

I like this one.

http://kosonorthamerica.com/shop/motorcycle-mx/mini-rpm/