Modern Vespa

I recently purchased a new GTS 300 Super HPE2 and after the 6,000 mile service I began to lose my top speed. It slowly dropped 12 mph over a two week period before it leveled off. Since it had just been serviced I really couldn't think what could be the cause. However, when I opened up the transmission cover what I saw concerned me. I have attached pictures of what I saw. I have never seen this amount of wear before, not even on my 2020 GTS 300 HPE with 36,000 miles on it. Clearly when they serviced my Vespa they did not inspect and replace the roller housing or the fixed driven half pulley.

In the past I have been forced to perform the maintenance of my Vespa due to poor quality work. This time was no different. I replaced the worn components and thought the problem would be resolved. Unfortunately it was not, I still did not regain my top speed. What could be the cause of this? Did the technician not tighten the valves enough and is one or more left open? Is this a speed sensor problem?

Looks OK to me except that the belt is not fully reaching the outside of the pulley.

Start with some more basic options:

I recently lost top speed on my Sprint and actually assumed it was because I'd put on a bit of weight... then it turned out my rear tyre was at 12PSI!

So check tyre pressures are where they should be.

Next would be trying to spin both wheels with the Vespa off to see if there's any drag from the brakes - stuck pads etc.

What level is the engine oil at? If it's overfilled = it could mean more fluid drag.

If all of these check out ok, I'd then move to what work was done on the service. Were the valves adjusted? Could they be at the wrong value?

Lastly, I'd also be tempted to unplug the battery for 5-10 minutes and then reconnect on the off chance it's something electrical that fixes itself with a reboot.

Did any of the worn components that were replaced; include any of the variator assembly (driving pulleys and rollers)?

If so were they the correct parts.

If the roller weights differ from standard that could cause a change in performance as could a clogged air filter.

Standard roller weight on GTS 300 (21x17) is 14.00g

Also if the variator half pulley is not exactly the same as stock (different profile or thickness) it could cause the drive belt to not ride at the correct height if ridden at wide open throttle.

Is it accelerating the same?
I'd be checking air filter and valves.

although 12mph is a lot I do definitely measure a change in performance with very worn pulleys.

Those pulleys are very worn. The question to me is why so worn after 10,000km - if was 30,000km and given a hard life then sure.

How about this idea:

Those are not the parts off your bike. It could have been an honest, but careless mistake. The mechanic put your parts in the wash bin, went to lunch, then grabbed a different part.

I had some warranty work done on my 23 HPE Super Sport at 4600 or so miles. While it was apart (oil sensor sensing switch), I asked Robot to go ahead and do the 6k mile service early. I got to see all the parts and my pulleys looked new. Not a lot of difference between 4600 and 6k miles to make it look as worn as yours.

My bike also had a little, hard to describe , vibration between 30 and 40 mph. This was fixed after the valves were adjusted (exhaust valves were tight).

Maybe the wrong washers were used or not in the right order? I know there was a specific way my 2012 had to have the washers.

Please share with the collective what the charge was for the 6K service?

My charge for the 6k service was $846.00. As for these parts not coming off my bike the part numbers match up with what they should be. I believe that they should have been replaced at the 6k service but were not.

As for the acceleration it feels sluggish from 0-30, like I'm towing 500 lbs of rocks. While 30-55 feels about the same with last bit very slow. I also had the rear tire replaced around the same time. I was informed that they recalibrated the traction control system but noticed some issues with it so I calibrated it myself and they were resolved. Perhaps they didn't balance the rear tire? would that have any effect on the top speed?

sluggish at low end can easily be ASR. ASR can be upset after a tire change or pressure change. recalibrate it (as you did), also try turning it off. if it's really wrong it could affect top speed, although if it was you'd see the asr light flashing while it's interfering.

Having paid that, I'd be straight back at the dealer asking what they've done wrong. Leave it to them to sort.

My guess is either sticking brake pad causing drag, ASR, transmission, or valves adjusted wrongly. Valves have a noticeable impact on mpg and power.