I'm hoping I found the right page to find help with my issue.  I have rescued a 1976 DT125C from my stepfather's property.  I know that it had been sitting out for a couple of decades but I wanted a puzzle.  I'm trying to figure out if it is salvageable.  It is somehow locked up but I don't know where the issues is.  I got the jug off and the cylinder, piston and rings are in excellent shape.  I took the clutch cover off and the plates are fine.  I see a little rust in some places but nothing that would keep things from turning.  On the other side, I am stuck trying to remover the cover where the clutch cable passes through and that covers the drive sprocket.  I have removed the bolts but the cover is stuck fast! The clutch cable is stuck and won't move.  I'm not sure what position it's in as the chain is so rusted, the rear wheel won't budge.  I'm wondering if the clutch is pulled in, would that keep me from removing that cover?  Is there something else I'm missing?  I can't believe there would be more to disassemble to get to the drive sprocket.    I can't remove the engine to work on it because the rear engine mounting bolt pulls out behind the cover in question.  Let me know if you have any ideas.  I really want to make this scooter run again. 
 

With all the screws and shifter removed, that left side cover normally just pulls off.... especially if you were to pull in the clutch lever.
Your stuck engine may have something to do with the starter generator being locked up (rusted from sitting out?)
--Ray

I figured I had all the screws out.  I still stop once in a while to double-double check.  I don't want to force anything.  It separates enough to get a box cutter blade but that's all. Does anyone have a picture of the inside of the left side cover so I can visualize?  All parts diagrams show it from the outside.  

It's a two piece cover. The front part outer part needs to be removed and then if I remember correctly there is another screw underneath near the clutch adjuster that holds the inner cover. There's also at least one screw towards the rear lower near the shift shaft that can be hard to see.

Follow where all the screws are in this link.
It's possible any dowels are rusted in & just hanging on.
Could actuate the clutch a little at a time on the clutch lever & tap around the cover to get it to move out until you run out of actuator movement but should help.
I don't see the dowels drawn there--only for the other cover but i'm sure there should be two & will be on both screws #5 if you can follow them--one top one bottom & sort of inline & supporting the actuator to stay inline with the pushrod.
Those two screws will be longer because of the dowels.

www.partzilla.com/catalog/yamaha/motorcy...125c/crankcase-cover
Also if you look through the inner cover you see a cut out which has a slotted rubber thingy.
They jump out then hide under the bench so be careful. I'll post a link to that as must be in the crankcase pic.
www.partzilla.com/catalog/yamaha/motorcy...c/cylinder-crankcase
Number 12

& Welcome from NZ downunder.

These are the best drawings I've been able to find as well.  The first drawing listed CRANKCASE COVER part #1 is the difficult child.  The hang up feels like it is hanging up on the right side lower part of the semi-circle ridge.  I can get a little separation along the top and around the left side while gently tapping around the cover.  The clutch is stuck in what I imagine is the "pulled in" position.  The cable is out of the clutch handle and the cable outer cover is loose enough to slide over the inner cable that does not move.  I have put penetrating oil down the hole with the clutch cable hoping to free it up so I can   Does anything from the clutch that's covered by the small cover need to be removed? (parts 18-21 in the CLUTCH diagram below) Seems like a little much to get to the drive sprocket.  I have a twin to this bike but the cover in question is missing.  I haven't studied it enough yet to see what I'm looking for.  If/when I get in there, I will keep an eye on part #12 rubber thingy!

www.partzilla.com/catalog/yamaha/motorcycle/1976/dt125c/clutch

I will keep you posted!
 

The clutch actuator doesn't have anything that could be holding the cover on.  In fact. like RT325 said, if you had the lever hooked up and all the screws removed, pulling the handlebar lever would help push the cover off. 

Ebay can be a good source of part pictures.

My guess without seeing it and assuming you haven't missed a screw, is crud/rust around the shift shaft is preventing the cover from sliding over the shaft?  Penetrating oil and temporarily reinstalling the shift lever and moving it up and down should help free it up.

Mark,

Thanks for that advice about the shift lever. I'll oil that thing up like bachelor party entertainment! I'll get started on that when I go home at lunch in a couple of hours.

JT

Yes, shift shaft as Mark said might be the answer i'd not thought of for sure.
Does the gear lever move at all.
If it doesn't move then ya gonna have to try moving it up & down & get some oil down in the shaft with the bike flat on its right side. Won't move far up & down because it'll be trying to change gear up & down.
Maybe remove gear lever then put a lever or piece of wood in behind by the sprocket & lift against it while tapping the gear lever shaft.
That can be fraught with problems as there's a circlip on the shaft in behind against the crankcase but i've done that on an RX125.
All that & with clutch operated to put maximum sideways on the cover.