i had a similar problen no top end power the boy's on this site,set me right. Check power value up is opening right up
if not reajust. loosen nut turn shaft down, it got a hole in it. trial and error thighten nut up. start motor ,rev it, with kip cover off you can see if it opening all the way out. that what i did to my, now it's got it top end back.
good luck let us know about it.