Can anyone tell me what is inside the split-cable (Throttle/Oil pump) junction sleeve and how the cables are connected therein? (pictures would be nice).
My throttle will not turn after years of disuse, and I think it is binding at the split junction sleeve.

Try this....

Just what I needed!
Thanks Deet!

Not sure what bike you have, but this guy sells cables.

hvccycle.net/throttle-cables/?sort=alphaasc&page=1

the cables besides the street 2 strokes listed are for both the 1974-76 DT250, 360 and 400 and the 1977-79 DT250 and 400. they don't sell the 1968-1973 Enduros apparently.

No they dont,

I confirmed with Motion Pro as long as you have most of the original cable setup, they can fabricate a replacement. He says they have most parts, only having to reuse fittings for some of the oil pump cables as they're NLA.

To the original poster, inspect the junction/splitter. If you see any burrs/gouges, use 1000 grit sandpaper rolled into a tube, very lightly sand up/down and rotate, slowly until the inner is smooth. Blow the splitter out with compressed air to ensure you get any debris removed.

You'll want to ensure the splitter is greased well, a big dollop of a high-quality grease, I use the JDM spec red grease. Also, you'll need a cable lube tool, and cable lubrication spray.

Take your time, see if you can get the cables lubricated (from the throttle, down to carb/oil pump) and sliding freely within the cable sleeves. Do not ham fist it or you'll snap the cable if they're binding. They all need to be working in unison.

I would not do this. It may limit travel. The return springs may not be able to squeeze the grease out of the way.

My repop RD350 workshop booked called for it, the old AHRMA racer Lyn Garland recommended it. It's the way I was taught.
Your results may vary, but I never had any issues with my twin using this method. It can't run dry, my original was packed with clear grease (tinted amber from age) from the factory.

With the above said, to clarify, and to expound upon DEET's comment, don't pack it full of grease. Just enough to lubricate the sleeve. Generous, but not too generous.