World Superbike Racer
Join Date: Mar 2013
Location: Woodbury, MN
Thanked 565 Times in 446 Posts
Feedback Score: 1 reviews
None of this happened until you changed the oil and went with a heavier weight, correct?
Did you stay with the same oil brand/type/etc. or did you change that as well?
With that many miles on a bike that's been ridden hard I would not be surprised the clutch is "questionable" and the change in oil is bringing that to light. Simply changing from 10w40 to 20w-50 shouldn't CAUSE a problem, but might bring something up.
The symptoms are classic worn clutch; not transmission, TPS or something electrical or it would be far more abrupt or more of a shock type thing. It's not unheard of to only have slipping in one gear or rev range because of load placed on the clutch at those times; and honestly how often are you in 3rd, 4th or 5th pushing 9k WOT on the street?
You have a few choices at this point, your call.
- Easiest and cheapest is to change the oil back to a 10w-40 and see if that fixes it or makes the symptoms disappear. $40, no need to change the filter, but pull it and dump it, get all the old oil out. It may "fix" it but prepare to replace your clutch soon if it does.
- Pull your clutch cover off and look at the plates, both metal and fiber; replace if necessary. $175 or so, I suggest OEM, but EBC, whatever quality aftermarket will work fine. You might just need fibers so pull them and inspect before ordering. Most modern bikes have plates in a specific pattern and placement for plates, KEEP THEM IN THE SAME ORDER AND ROTATION ACCORDING TO THE MANUAL.
- take it to a shop with a dyno, have them recreate it and see what they think.
I've done all the above and had all the above work for me on various bikes Over the years.