Trouble setting rear derailleur

[aquaregia]

I'm having some trouble adjusting my rear derailleur. I've followed this guides on this site and others but I'm still not quite getting it right. I have a cheap mountain bike with a seven-speed Shimano SIS that I can shift down just fine, but shifting back up is a bit tricky. Specifically, if I shift once up, nothing happens, however after that it shifts fine. For instance, if I try to go from 1st to 2nd I have to click twice, 1st to 3rd three times, 1st to 4th four times, etc. The final shift always returns to 7th, even if it means skipping 6th. I've been riding it by shifting up and down an extra time each time I want to shift up, which results correctly, but it's sort of a pain. I believe I followed the instructions correctly, but as I'm having problems I suspect that I'm wrong. If I tighten the index tensioner further I scrape against larger sprockets. If I loosen it a little, it starts skipping 2nd gear on the way down.

Thanks for any suggestions

[TESTUser111]

Your derailleur hangar (where the derailleur mounts onto the frame) may be bent. This is a common problem that can happen if the bike falls over on that side.

A bent hangar will cause irregular shifting problems like you describe. There is a special tool required to re-align it. Your local bike shop should be able to check it for you for a minimal fee.