Hello hello,
am I right in understanding that the DT125E 1978 MX only has adjustment at the clutch cable swivel nut, at the handlebar.  Once this 'slack' is taken up should the next step be to remove the clutch cover and 're-adjust' the clutch hub lock nut?  And also check the plate wear I guess.  It's just that the cable is wound out quite a bit and and there is no secondary adjustment further down the cable.  I'd just like to be more aware of how it all sits right.  Cheers

(also is it better that I post this in the 1977 MX bikes section?)

Link below shows only an adjustment on the clutch pushrod at the pressure plate #14.
If that needs adjusting it would only be to bring arm #20 back to a good operating possition.
I'm sure there'd be a little bit of scope to go back further behind the mark with the arm if you had run out of cable adjustment.
Bit of a pain to have to go in there though. Is the clutch still doing it's clutchy thing or is there something going on other than adjustment.


www.partzilla.com/catalog/yamaha/motorcycle/1978/dt125e/clutch

It's important, if not quite critical, to follow the process shown in the manual. 

There are really two factors...  one is that the clutch arm on the engine must "engage" the internal pushrod fully when the lever is at a certain angle... this is important because if internal adjustment is off much, clutch will not disengage fully. 

The second factor is cable freeplay.  Sometimes someone will reduce "external" (cable) freeplay to help clutch release fully when lever is pulled. Then you can end up with a slipping clutch that wears out very quickly. 

I start by removing the cable from the lever on top of the engine.  (Yes, remove). Now push the lever forward against its spring until pretty solid resistance is felt which means you've taken up all the "internal" freeplay and moving the lever forward more (which you probably won't be able to do with your finger) would start to lift the pressure plate and allow the clutch to start slipping.   

Yamaha has provided a "nub" in the top of the case that the lever should line up with when pushed forward.  If it doesn't line up pretty good, then you MUST remove the clutch cover and make an internal adjustment!  No amount of diddling with cable freeplay can make the clutch work at its best if the lever angle when internal freeplay is removed is off much. 

(While strictly not necessary to disconnect cable from lever, it's much easier if you do in my opinion and only takes a second.)

If the lever is not lining up properly with the nub, you adjust it as follows:  Keep forward pressure on the lever on top of the engine with a finger...  as you turn the adjustment screw in the center of the clutch "in", the lever on the engine will move back...  loosen the adjustment screw and the "stop point" of lever will move forward.  Remember this is with you pressing forward on the lever on top of the engine!  Simply adjust screw in or out until lever aligns with nub.  Tighten adjuster screw locknut

Now the linkage will be in proper alignment and you can simply set the freeplay at the cable...  And once the internal freeplay is set correctly, it usually doesn't change much during normal riding.  I've gone for years before having to adjust the internal mechanism to get the lever geometry correct by lining it up with the case nub.

I guess after following the correct procedure & your cable is running out of adjustment then going to have to shorten the inner cable which is do-able if you can heat it to melt the solder & move it along a little then resolder. Youtube it. Next problem is if the top cable nipple is that alloy composite crap but usually the bottom end nipple is brass. One more random thought 'is' if the clutch fibers are burning out then the clutch compresses more which reduces your cable play as the arm moves back. But that's irrelevant to what you're hoping to achieve with cable adjustment. "Ignore my ravings" lol. Mark has is down to a T with his instructions.

Thanks guys. So to clarify you line up the clutch lever cable holder on top of the engine with the clutch cable removed and pushing the lever (cable holder) with your finger to get resistance, then adjust at the clutch hub if necessary. Under load ie normal operating condition my 'raised boss' is lined up, but I am worried about the slipping clutch as you say as the cable is quite far wound out at the handlebar and releases with little pull (which is great) but doesnt leave any room for any further adjustment - I think I'll keep riding but I guess like you say as the plates wear i'll have to at some point pull the cover and reset (and probably also have to install new plates)
thanks so much, I believe some things are getting clearer for me

To be clear. The clutch actuation lever has a pointed end. The tip of the point is what lines up with the nub. Not the lever in general.

As with any cable operated system, the actual adjustment is done at the bottom of the cable. In your case, inside the clutch cover.
The handlebar lever end screw and lock ring should only be considered as a means of fine tuning the handlebar lever free play adjustment while on the go.  It should never be used as a general clutch actuation adjustment.

Pic from manual



Cable could be stretched too.