clutch slippage and fluid type M8 114 2019

[KatalogKarl]

Need a little input on what to use here. 2019 M8 114 FXDRS. Local guy who I helped with his shovel. Got himself one of these. Exhaust, Air filter and installed air/fuel program change. Bike around 6k mileage. Was TEST bike from dealer here in west central FL. Told it had some mileage on it. I am new to this engine/electronics/design. Still riding shovels. So- after this guy loads all this into his bike a runs it as such for 3 months he asked me to ride it and note if clutch may be slipping. No issues with 1st and 2nd. from 3rd up when around 2500-2800 goose it and a slight slip felt.. He had me take clutches out to inspect disks and steels. No warpage or burnt steel or glazed discs. So a possible clutch spring problem? feels like it. Also what is decent primary/clutch fluid used? In my shovel (ATF) is used. This bike is crisp, torquey and pulls good thru all rpms and gears. Just not a fan of leaning down as is what happens on sport bikes. Just some input as I said this type of configure of a (HD) is new to me. Thanks Karl

[KatalogKarl]

Needed to add. so I found out what tuner is installed on this scoot. Its a Thundermax tuner. Do not know if this makes a difference but looking at what it is and cost a considerable performance part. As  this mechanicals is NEW to me. 

[kd]

I think the tuner has likely responded by making changes that provide more power and the clutch is now struggling with the new increased torque.  The Thunder max is known to be good at adjusting to new condition input and probably what has happened.  If the clutch is adjusted properly and not damaged a heavier spring will probably resolve the slippage.

Added later

You may also want to look at the extra plate or surface clutch disc options out there to avoid a heavier lever pull.  More money but maybe more desirable outcome if the heavier spring is not suitable to the owner.  The spring is a cheap option and no real $$ loss as a test.

[KatalogKarl]

Thanks KD. Seems to be a common happening when engine changes are made. Found stronger springs and on order. Also did some research here and a  WTF moment when I looked at some dyno runs and afr blogs. Bolt on and with the right tuner and with the right person doing it awesome and unexpected results. Admit I may not be able to handle some of these power curves I viewed. Guess I am comfortable with my dinosaurs(shovel). Thanks.. karl