OK. I would like to made it clear first - I have Piaggio X8 400. Is has exactly the same engine as MP3 400, but is approx. 40kg lighter. I want to share my results with you (despite not having MP3, unfortunately), because this forum has the best resources about transmission tuning for this engine - IMHO. So I would like to give something in return for the knowledge I got from you.
I decided to test acceleration for different sets using custom onboard computer. Computer calculates speed counting impulses from the front wheel. It has good accuracy - 20cm per impulse. It gives 14 impulses per second at 50kph, which is enough for mu purposes. What is more important, it calculates speed, not estimates speed like GPS based applications - 99% of GPSes gets data once a second which is too rare to measure acceleration accurately - at least when it comes to scooters, not glaciers. Here's a shot of my computer's display.
And here's a link to a movie when it shows a screen with performance tests: http://youtu.be/JYPWZkKn7HY?hd=1&t=4m50s
Tables below should be quite self-explanatory. I made many runs on each setup but wrote down only significant results. The last column shows theoretical best result based on best intervals from different runs. Best intervals are shown in green.
1. Stock setup, cost - 0$
2. Fuzzy washer, cost - low, I don't remember
3. Dr. Pulley sliders 16g, cost - over 60$ AFAIR
4. Fuzzy washer + Dr. Pulley 16g, cost - like above
5. J.Costa, cost - around 300$
The best bang-for-the-bucks ratio is Fuzzy washer + Dr. Pulley.
Fuzzy washer - should be used with lighter weights to know the difference.
Dr. Pulley sliders are very good, if installed properly. I managed to fit it incorrectly at first, despite using such sliders in my previous scooter for years.
Fuzzy washer + Dr. Pulley - best times.
J.Costa - it is nice if you like to go WOT all the time. It gives you this warm feeling in the stomach, like you were invincible . But it is annoying when just cruising at lower speeds, because it is revving high even when you don't want to. But results are very consistent - like 6,5 seconds to 80 kph and 9,4 second to 100 kph almost every single time.
I am going to measure if it would be possible to fit fuzzy washer with J.Costa without much risk for the belt.
Riding with sliders without washer was most enjoyable for me.
Thank you for your patience if you read down here, I hope you did not hurt your eyes (or brain) with my terrible use of English.[/url]