Bicycle Mechanics - Suntour Accushift b-tension equivalent?

So my commuter bike started making a racket recently, and when I went to inspect it, it appears the rear derailleur (suntour accushift plus) is actually sitting on the two lowest cogs while riding, causing it to jump up and down and make a whole lot of really annoying noise. It didn't used to do this, so something has changed recently.

I figured it would be a simple b-tension adjustment, but upon closer inspection, it doesn't actually appear to have a b-tension adjustment screw anywhere. Does anyone know if there's any equivalent adjustment I can make, or is it broken for good? I've been considering upgrading the bike to 105's anyway, so maybe this is kid of a sign.

thanks!

Hello. can you post a pic or two? and is there a model name other than accushift? it may if fact be broken. if your shifters are in good condition you may be able to just replace the RD for now and a 105 should index for you without much trouble

That probably would help, no?

They're Suntour Edge accushift 4050, as far as I can tell. Attached are pictures- you can see how far forward of the axle the whole armature sits.

Will a 105 rd work on a 7 speed cassette? If it is broken, I was just planning on not running in the granny gear until I could get everything sorted, but I would prefer to fix it as I'm a little short on fundage right now.

I had an Edge Accushift 3040. Slightly different than yours probably, but during re-installation after cleaning once I ended up accidentally breaking off a tab on the derailer. This tab normally went against the derailer hanger tab, the one that sticks down beneath the threaded hole (and what a "b-screw" rests against). I discovered that it was needed to keep the derailer from riding on the smallest cogs. I think chain tension worked to make riding the larger cogs OK. I couldn't think of a way to get the tab reattached and I didn't really want to run a shorter chain in hopes that that might work OK so I just bought a used Suntour GPX rear derailer on eBay.

A Shimano rear derailer won't index correctly with Suntour levers. I tried the 600 SIS I had laying around but could not get it to work.

That's what I expected the case to be when I first noticed things, but upon closer inspection there is no threaded hole/b-screw at all, or anything that outwardly appears to be broken off. That's why I'm so confused- there don't appear to be any adjustment screws at all besides the H/L stops. I was hoping someone had had this model of RD before and knew what controlled the tension, because I can't even figure out how it was done in the first place.

On my 3040, there was no adjustment for b-tension. It was fixed by the presence and size of a tab. The tab was made of soft steel and very easy to break off. I bet your derailer has (or had) such a tab.

Ah, I see what you're saying now. I gave it a good once over looking for anything that looked like there used to be a tab that had fractured off and didn't see anything, but who knows.
I took it out and rode it yesterday and it seems to work ok, so no worries- it just makes more noise.

I'll run it till it breaks and then upgrade- if it's actually broken, it's easier to justify to the wife.