AK550 J Costa fine tuning

[ktienation]

Hello Lads and Gents,

I just recently bought my AK550 and I absolutely love it (I've been riding a DT300 for the last 8 years with over 25k miles on it).

My scoot is equiped with the aftermarket J Costa variator, and I knew it has specific characteristics (high revs etc). What I didn't expect (however I should have, as I test driven a few AKs at the dealer shop before buying) is that the AK clutch catches rather high (on mine first signs of clutch engageing comes at 4500 rpm). The above mix results it the fact, that starting from dead stop or even accelerating ie from 15 MPH or 30 MPH (doesnt matter) comes with the revs going up to 6-7k (even if accelerating very softly).

Just to make it clear, I love the acceleration and 7k at WOT is something completely normal, however, it would be really nice if delicate starting from a dead spot or delicate accelerating would come with 1-2k less rpm.

Now the question: how is the best way to do it (I am ok with jeopadizing the performance a little, as the scoot has more than enough acceleration for me in every speed range). Would you start with buying heavier sliders for the J Costa? My first thaught was just softer springs in the clutch, but that i noticed this one has not a simple centrifugal scooter clutch but wet multidisc, so it would be way more difficult if no impossible in modding it to engage at lower rpm.

Thanks for all the tips and thaughts.

[Stig / Major Tom]

Maybe you could explain your situation and put that question to them?

https://www.jcostavariators.com/index.php/help

Stig

[rjs987]

Not sure how to help here. My AK is totally stock and the clutch starts to engage at much MUCH lower rpm. It usually goes to around 3500 rpm +/- during a normal start up. I usually don't see over 5500 rpm unless I really gun it. But I'm a conservative rider even if I do usually leave traffic behind from a stop light. I am entirely satisfied with the acceleration of the stock setup. But if you are used to the performance of higher rpm before the clutch kicks it might be too much to go back to the stock configuration. Heavier rollers/sliders might bring down the initial rpm. Is the clutch stock? Unlike the clutch on smaller scooters on which the clutch is on the driven pulley of the CVT on the swing arm, the AK has the clutch on the other side of the engine somewhat remote from the CVT yet the output shaft of the CVT still inputs to the clutch so the operation is the same. If you go with heavier rollers/sliders consider also going with a different contra spring to match.

This is all guess work so do more research on it to be sure of this.

[ktienation]

Thanks for the replies. Well on my downtown I had little bit lighter than stock dr. Pulley rollers which give me wot at 6500 rpm (peak torque) instead of stock 5500 but apart from that all worked as stock. I know that the J costa works this was that it revs much higher and this is due to the construction of the vario. I don’t know if I have stock clutch but I believe it’s highly probable.

I have the feeling (but only my feeling) that in the Ak the clutch works a little different than in the DT, in particular, doing static tests with the cover removed I saw that the clutch engaged before the vario started to “change the gear”. Here in the AK I believe it needs specific rpm on the clutch input shaft and with stock the vario already changes the “gear” before engagement (the transmission belt’s output disc is much bigger than the input) and the J costa does not as it needs much higher revs to start changing the gear.

I think stiffer contra spring will offset higher slider weight and it will give same specs. I will try to buy a little heavier sliders and see if I am right, fortunately they are not very expensive where I live. 1k less for clutch is all I need and would be nice to keep same revs at wot for performance.

[bgjosevski]

Thanks for the replies. Well on my downtown I had little bit lighter than stock dr. Pulley rollers which give me wot at 6500 rpm (peak torque) instead of stock 5500 but apart from that all worked as stock. I know that the J costa works this was that it revs much higher and this is due to the construction of the vario. I don’t know if I have stock clutch but I believe it’s highly probable.

I have the feeling (but only my feeling) that in the Ak the clutch works a little different than in the DT, in particular, doing static tests with the cover removed I saw that the clutch engaged before the vario started to “change the gear”. Here in the AK I believe it needs specific rpm on the clutch input shaft and with stock the vario already changes the “gear” before engagement (the transmission belt’s output disc is much bigger than the input) and the J costa does not as it needs much higher revs to start changing the gear.

I think stiffer contra spring will offset higher slider weight and it will give same specs. I will try to buy a little heavier sliders and see if I am right, fortunately they are not very expensive where I live. 1k less for clutch is all I need and would be nice to keep same revs at wot for performance.

Hey, I just saw this thread. Did you ever replaced the rollers with heavier ones. I have the same issue. I mean it’s not an issue but I would like the rpm’s to be lower if possible. I have the stock variation and planning to install 19 gram rollers, instead of the 17.

[rjs987]

Wow. 2 gr less will result in a very noticeable difference. Yes, the RPM will be lower. But so will the power... and acceleration. Due to that I'm not so sure the mpg will improve. It might take burning more just to maintain the same speed at a slightly lower RPM. Torque is a function of RPM and output power (and a few other factors). Perhaps better to change to 18 gr from the stock 17 gr.

[bgjosevski]

Wow. 2 gr less will result in a very noticeable difference. Yes, the RPM will be lower. But so will the power... and acceleration. Due to that I'm not so sure the mpg will improve. It might take burning more just to maintain the same speed at a slightly lower RPM. Torque is a function of RPM and output power (and a few other factors). Perhaps better to change to 18 gr from the stock 17 gr.

Hey Bob,

I won’t probably do it:) dealership told me that they will void my warranty:)
Anyways, today I was riding in the rain mode and it got me closer to what I like. Rpm stays at around 3500 at steady speed of around 30-50 mph.
Acceleration is a bit slower but it doesn’t bother me. Now I can ride 30-40mph and the engine is a bit quieter.