Modern Vespa

Hi,
I need a little help here.
Most importantly, I need to know if my reasoning works.
I have a Vespa Primavera 4T3V from 2018.
I've slightly upgraded it with a Multivar and used the 6.1g weights that came with it.
I've replaced the CDI with an unrestricted Malossi CDI.
I thought it was running quite well until I switched to a Malossi MHR X K drive belt.
The belt is 765mm long instead of the original Piaggio belt, which is 756mm (I believe).

Here's my theory (bear with me, this might get messy).
Longer belt = it goes higher up in the variator, allowing for a higher top speed.
…but I feel like the acceleration got worse and that the Vespa became weaker after I made the switch… Also, the top speed was about 55km/h (34 mph).
Shorter original belt = doesn't go as high up in the variator, making it a bit slower, but I felt like it was quicker, stronger and faster…

So here's my question: does this seem logical?
Should I go down to 5.5g weights and keep the longer drive belt to improve acceleration, revs, and power at the start?
Or should I keep the 6.1g weights and switch back to the shorter original belt?

My ULTIMATE goal are that I would like to be able to reach 65km/h (40 mph) without doing anything more than adjusting the belt and variator.
I want it to be strong at the start, and I don't mind if it takes its time to reach top speed.
Is this even possible?

I need to take it to the workshop for servicing soon, and I would like to have the right parts with me.
Unfortunately, I don't have a place to work on it myself, so the workshop is a must.
Sadly, this doesn't leave much room for experimentation…

I do not see the point in applying a longer belt, assuming the width is the same.

Both the driver pulleys, the variator at the front, and the driven pulleys at the back have a fixed width range they can achieve. And that width range is mechanically defined.

I would expect the length of the belt is such that it fits the starting conditions with the driver pulleys furthest apart and the driven pulleys closest together, but still with enough tension on the belt to prevent it from slipping.
If you mount a longer belt I expect there will be slip in the system.

go back to the OEM belt and all your issues will be solved

The longer belt will not reach top speed
It will go to the top of the drive pulley
But
It won't go to the bottom of the driven pulley

Is that a reasonable speed goal for that model?
55 to 65kph is a big step up.

There won't.

What's slowing the bike down is not the longer belt, and for people who don't understand the reason for a longer belt, or an over range transmission, there are a lot of places you can learn why this is common in 50cc and T-Max setups. Youtube is one of them. Malossi also has some videos that may help you understand this. A longer belt helps overall performance not only because it goes higher on the front pulley at the end of a long straight road, but because it is higher in the rear pulley while the belt moves through the middle of the front pulley, where the performance happens.

What cost speed and acceleration is that the roller weights are too heavy for the setup. The Malossi variator fits everything from the dog 2 valve to the four valve, to the 3V in bikes as different as the Scarabeo 50 the LX50, the Typhoon 50 and the Primavera 50. Most of hem have different OEM weights, so it's not to be expected that the variator is set up optimally for all of them. It is likely set up to install it on a motor with a big bore kit. Going to a 5.1 or 5.5 will allow the engine to both rev freely up into the powerband and take advantage of the advance curve and higher rev limit in the new ECU.

So, it would be a good idea to change to less heavy rollers. Good.
I might just try that. I really dont know.
The speed i mention is the one on the speedometer. The actual speed is 5kmh lower according to gps.
So 55kmh is in reality 50kmh. I would really like if it could go up a bit more than that but its not a big issue.
I often take trips longer than 70km and a little more speed could do alot.

The belt i use is a "kevlar" belt and after i got it installed i read that the belt is so stiff and could actually make the performace worse.
It will hold "forever" but its not optimal for an weak moped.

So i might just change it to an 764x18,7x8 regular belt instead of the kevlar one.

Does that seem correct or am i just on the wrong path?

After i replace the stuff i will post a conclusion of the result here.
I think it might help somebody else in the same situation and with the same thoughts.

You also might look to change the clutch spring out for a stiffer one. This might help engage the clutch from a standing start.

Ok, today i got my baby back from service.
The belt was replaced to the belt that i coult lay my hands on: 18,7mm wide and 764mm long.
It was 1mm shorter and 0,2mm wider.
I went with the 5.5gr weights instead of the 6.1gr.

What happend?
The vespa went from 55kmh to 62kmh ant that is nice.
The gearing felt more consistant and even.
But... I have the fealing that the rev is a litle low and not in the right powerband. Actually i feel that the rev is a little lower than before.

So, should i just try with 5gr weights instead to get a little bit higher rev and therefore a little more power?