Maybe somebody would know this. My friend has a bike and it will up shift yet not down shift like 50 percent of the time. What would cause this? At first we thought it was the spring(that pushes the lever back up) causing the issue by sticking. Replaced it and still there(Dealership told us it was the issue).

His wording:
"It shifts nice but down shifting sometimes it doesn't down shift. It just stays in place till I rev it up and then it down shifts."

Help would be appreciated.

-Jason

 

I think I figured it out. Shaft spring has gone bad