Modern Vespa

I have two GTS 300's. One is a 2010 and the other is a 2012. When both were stock (I've since made some mods to the 2012), the 2010 performed noticeably better than the 2012. The 2010 accelerated faster and had a higher top speed. I could do in the 80's with the 2010 but only 70's with the 2012.

Has anyone noticed a performance difference between the older scooters and the newer one's? Any idea what might explain the difference?

Same mileage on both scoots?
I'm assuming you've made the apples to apples I.e. same variator weights, same gear ratio, both have clean air filters, good spark plugs, same belt condition and size?
Gotta be transmission or engine health differences?

I would think so as well. There have been several iterations of the Quasar engine, but I think the 2010 and 2012 278cc engines are the same.

Accurate speedometer.

Everything on the two bikes is the same, even the mileage. The older one just runs a little better. I can't figure out why. I don't think its the speedo. You can feel the difference. I bought them both used so maybe the prior owners did something. But I have yet to figure out what it is.

Would belt condition affect speed? I noticed the variator on the newer bike was much dirtier inside than the older bike (again, same mileage). I don't know where it all came from. Maybe the belt in that one is wearing faster for some reason....

Yes belt condition will effect speed - if its worn and has become thinner or stretched out your max gear ratio is lowered. Your dirty variator and clutch are telling you that something is wrong with your driving pulley (variator) or driven pulley (clutch). I would pull it apart, clean and scuff up both pulley surfaces. Make sure your air scoop is unobstructed so the belt can cool. Your varator weights should also be checked for flat spots and the correct weight. 13 to 15 g for a 300 cc. Reinstall the belt and let it seat properly by not driving to hard or to long for a week or two. May be good to just replace the too.

What colour are they?

It is remotely possible that the earlier one has 13.5g weights and the later one has 14g.
There is a suggestion on a German site that the weights can be 13.5 or 14 but it is a longtime since high school German.

I like how you think.

Drive belts don't stretch out, but a longer belt would go higher in front and lower in back, resulting in higher, not lower, top speeds. A dirty variator and clutch tell you that a bike is being ridden, not that something is broken. Repair manuals don't tell you to scuff up the pulley surfaces, or they wouldn't be polished when new. But if you have a groove worn in them, that will affect top speed. The "correct" factory weights for a GTS 300 are 13.8 grams, not 13 to 15, and you aren't going to properly seat a belt by riding gently for a couple of weeks, because you don't seat a belt.
But belts do get thinner as they wear, and that will affect top speed.

Fully agree with Motovista. What he says ^^

The only other thing that affects these engines is how they are 'run-in'. If the slow one was babied too much and never or rarely went over a certain rev band during the previous owners use of the bike, that will slow the motor and have an effect on power output. This tends to happen on bikes that are mostly used in towns or cities. The effects I've seen on the dyno can be quite dramatic with less power being produced.

Or...the other things that can harm the engine power output is running it flat out from new without observing the running in rules. Owners think they are making it a 'fast' bike because INITIALLY it WILL go slightly faster than another bike with the same engine and miles that's been run-in according to the book. However, that slight advantage doesn't last long as the bike being run-in according to the book method slowly becomes faster and faster and will eventually overtake the performance of the 'fast run-in' bike. It'll be more mechanically reliable over big mileages too and nearly always will use less oil long term.

I may try changing the belt, but the bikes only have about 2,500 miles on them, so it seems really early to do that.

I bet the the engine run in theory is the reason.

The older bike looks like it was much more used than the newer one. I bought it from a guy from North Dakota. The engine compartment was really dirty, like he rode it off road or something. In fact, the older one looks so used I wondered if the odometer was accurate.

The newer bike looks pristine, like brand new, except for a few dings and scratches. I got the impression that one was just used around town here in Florida. When I got it, it was pretty much spotless inside and out.

If they're both the original belts, and knocking on 10 years old, it wouldn't be too early for me. No idea at what age of a belt means it's too old, just that it's cheap insurance in my mind. Same for tires if they're original. Just my thoughts, and I'm not a mechanic...

6 years belts start to deteriorate. So it's time.

I did not know belts deteriorated with time. I've been changing everything else out, since there is no way to know with a used bike what has been done and what hasn't. So I'll add belts to my list.

Thanks again!

Instead of guessing what seat of the pants cannot ever fully prove, how about a GPS reading?

[quote="Motovista
Drive belts don't stretch out, but a longer belt would go higher in front and lower in back, resulting in higher, not lower, top speeds. [/quote]

Not true. A longer belt would cause the belt to ride higher in the variator, causing it to rub on the housing with the resulting oil leak. And if it did stop at the top of the variator it would not be so deep in the clutch pulley, so you would get a lower ratio, not a higher one. If you take it to the extreme, you would have the belt riding at the top of the variator and at the top of the clutch pulley, and a constant 1:1 ratio.

A shorter belt, eg. a GT200 belt in a GTS, would be a more interesting experiment. At take-off it would be riding lower in the variator, giving a lower "low gear". Then at speed when the rollers have forced it to the top of the variator, it would be deeper in the clutch pulley, giving a higher "high gear". So you should gain at both ends. I have done this on my GTS300, and it works.

Mike

Edit: I believe both Polini and Zelioni recommend shorter belts with their variators.