kymco zx fever 50cc advice on improved acceleration

[kirah65]

Hi so im looking for some performance advice on my kymco zx fever 50cc not 100% on the year as i got it used but my guess is around early to mid 2000s.

What i want to do is overall improve its acceleration or more of having a constant decent acceleration im not looking to be able to pop wheelies or anything like that.

Right now the 0-10km/h is a bit slow ( becomes better once warmed up ) which is fine the acceleration from 10-35ish km/h is fantastic but.

Once it hits 35km/h its like im driving in glue it will slowly crawl up to a peak speed of 55-60km/h going down hill helps quite a bit and im more then fine with that top speed i just don't like that it takes a eternity to get to that point.

Things i have done Removed all factory restrictions got a brand new CDI with the rpm limiter removed switched the exhaust to the Tecnigas silent pro pipe made sure it did not have any plugs and lowered the variator weights from 8g stock to 6g and installing a unrestricted drive boss

(which is what improved the 10-35 range it was just slow all the way with the 8g weights but same top speed)

it still uses the stock air filter box i tried to use a " performance " filter but it ran quite a bit worse and made way too much noise so i would like to stick to the stock filter box the filter it self is brand new.

So my guess is that the CDI while unrestricted has some sort of rpm safety where it will still protect the engine from damage should the rpm's reach way too high.

And i lowered the weights too much so it reaches that rpm point before hitting its top speed so im considering slightly increasing the weights from 6 to something like 7 or 7.5.

And maybe changing the clutch springs tho im not sure if i should get harder of softer springs and i have no idea what i have mounted atm.

Any advice and tips are welcome and what do you think should i get harder or softer springs if so with in what range would you recommend or maybe there is something i should look out for?

As the winter season is getting closer and im planing on doing some body panel repair and touch up the paint so it all needs to come off during the off season so if there is anything i need to keep a eye out for do let me know.

[repherence2]

get a sport big bore kit.

in the meantime, maybe a performance variator would make that difference you seek.

how deep into the rabbit hole are you going? how much are you willing to put in to achieve what you want? the more performance you seek, the more "tuning" you have to do. and "tuning" involves working on the CVT and carb. a lot of times tuning involves trial and error.

[aeroxbud]

Stiffer clutch springs will definitely improve your initial take off. Get a pack of three different strength springs, so you can see what works best.
A variator might help like said above. It might give you a couple more miles on top speed. But more beneficial would be the more constant shifting.
Buy a set of tuning weights too. Even quarter of a gram can make a difference. It's all about trial and error. A tachometer would help.
The silent pro losses power fast after about 8,700rpm. But has good power from about 7,500rpm. Get the CVT set-up in that sweet spot.

[repherence2]

Oct 23, 2021 10:05:14 GMT -5 aeroxbud said:

Stiffer clutch springs will definitely improve your initial take off. Get a pack of three different strength springs, so you can see what works best.
A variator might help like said above. It might give you a couple more miles on top speed. But more beneficial would be the more constant shifting.
Buy a set of tuning weights too. Even quarter of a gram can make a difference. It's all about trial and error. A tachometer would help.
The silent pro losses power fast after about 8,700rpm. But has good power from about 7,500rpm. Get the CVT set-up in that sweet spot.

So very true how .25 grams can make a big difference. I have experienced it myself. That's why i have a ton of roller sets in .25 gram increments. Allows for really fine tuning the variator .

[kirah65]

Alright I have a set of weights at a range between 8g all the way down to 5g in 0.5g steps.

And I picked up a set of these www.twostroke.se/polini-kopplingsfjaderskit 4k 5k 6k and 7k rpm

What combo do your guys think i should I try first?

[aeroxbud]

Try the medium strength springs first. If you get seamless acceleration, it's good. If it lags a bit try the next harder springs.
Only change one thing at a time. Otherwise it's hard to know exactly what's working.

[kirah65]

Right bit of a update i gotta get a 39mm socket for my impact driver to remove the flat nut thing holding the clutch to the drive pulley thing together it cant be too easy now can it.

i did however manage to spot that there are currently yellow springs mounted to it probably from the previous owner if they are the same brand as the kit i got then they are rated for 6k rpm.
So my guess is that they are too stiff so i will start with the green spring one step below rated at 5k rpm see how that works maybe change the current weights as well from 6 to maybe 6.5 or 7g.
I do believe my model is suppose to have 7.5g stock but the ones that where paired with the current springs where 8gm.

also seems like a odd weight to spring setup but i might be wrong

[aeroxbud]

The silent pro doesn't start making good power till 7,500 rpm. On the Piaggio it's making about 4.8hp at this revs.
At 6,500 rpm it's making only 3.4hp. At 5,000 it would be even less.
But you are right to be using springs you know the rating off. Then you can gauge how much better, or worse they perform.

[kirah65]

Oct 31, 2021 15:12:42 GMT -5 aeroxbud said:

The silent pro doesn't start making good power till 7,500 rpm. On the Piaggio it's making about 4.8hp at this revs.
At 6,500 rpm it's making only 3.4hp. At 5,000 it would be even less.
But you are right to be using springs you know the rating off. Then you can gauge how much better, or worse they perform.

hmm but the springs effects the take off speed right? im not sure if you should base the springs on peak exhaust performance as i dont have a way to read the rpm's just yet but if im suppose to base them on the peak rpm of the exhaust then maybe i should go straight to the 7k rpm springs?

[aeroxbud]

The springs will not let the clutch out till they reach a certain revs. After that the variator controls the revs, till it runs out of travel.
If the springs are too soft. It's like the rollers are too heavy. The rpm on the springs is approximate. Different clutch shoe weight, or angle will effect at what revs the clutch engages. That's why a lot of manufacturers just quote spring strength, not revs.

[kirah65]

Alright replacing the spring significantly improved things but the acceleration still slows to a crawl at around 40km/h but at least I can cross roads at a decent speed now.

So what would be the next best step variator kit that includes everything for the front part of the variator as well as one of those larger springs for the clutch in the rear.

Or somebthing like a 70-75cc cylinder upgrade kit?
Or maybe 60cc honestly I'm not sure what would be the best

[kirah65]

Also something i noticed when i was replacing the clutch springs is that the large clutch spring had almost no tension to it.
And once i re attached the big nut that holds the two halves together there is almost no flex to it what so ever like watching youtube videos the drive belt is able to be pushed in quite a bit when they put it back on.

While mine where just rock solid and i had to fight a bit with the drive belt to go back on could it be that the main large clutch spring is just so worn out that it its not working properly and needs to be replaced?

and if it needs to be replaced should i get a stock spring or a slightly harder one as i have done some mild tuning so a slightly harder one might make it run better?

www.youtube.com/watch?v=2XRQ-5nqKlg the video in question like you can see he is just squeezing the as he says in the video torque drive but mine dose not move and no where near as much as in the video.

[aeroxbud]

With the clutch bell off. You should be able to squeeze open against the spring using both hands. It should be a fluid motion, with no binding.

[kirah65]

Nov 8, 2021 14:49:13 GMT -5 aeroxbud said:

With the clutch bell off. You should be able to squeeze open against the spring using both hands. It should be a fluid motion, with no binding.

Yeah I figured but mine only has a tiny bit of movement like maybe 1 - 2 mm at most so the spring must be shot should I get a new stock spring or one that is slightly harder?

[repherence2]

I would take apart the rear pulley and check the pins and slots. Seems like your rear pulley is binding if you can only get it to open 1-2 mm when you try to squeeze it open.