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The method that works well for getting about the same tension on the shifter cables is to hand tighten the adjuster bolts as much as I can without putting lots of oomph into it. Then I tighten down those lock nuts while trying to not turn the adjuster bolt. The cables are evenly adjusted, which is important so they don't jump out of gear, and there's very little play in the shifter. It goes into each gear pretty smoothly and confidently.
The barrel adjuster is only for taking up a limited amount of cable slack. When you run out of adjuster room, turn the barrel adjuster back down to minimum thread, but do not bottom it out. Your clutch cable should now have some slack that needs to be taken out:

Look for the clutch lever on the bottom of the engine. The clutch cable goes to this lever and a bolt type cable clamp. To adjust, you loosen the bolt on the clamp (the right size wrench is in the tool kit that came with the scooter). grab the cable with some pliers and pull the slack out of it, then push the clamp up against the lever. Don't push the lever itself otherwise you will partly disengage the clutch when it is supposed to be fully engaged. Using your own third hand, a third hand tool, or a friend's hand, tighten the bolt. The clutch should be adjusted at this point. Now try riding. If you get that whining sound, and the gear change is more notchy than normal with the lever all the way out, then there is still too much slack. 
If clutch cable adjuster bolt/assembly snaps off

It's a right-hand thread, meaning that if you turn is counter-clockwise
(from either end) it will come out.
If there is a portion of the hollow tube extended beyond the casting, you
could saw a slot to accommodate a screwdriver. If you have an "easy out"
that would be perfect for this job, unfortunately most people don't have

Soaking the part first with some penetrating oil and heating the aluminum
casting will help. Do this several times before trying to remove it. If one
end has damaged thread, you do not want to screw these damage thread through
the body, they will damage the internal threads in the aluminum casting.
Because of the hole through the bolt, this part is more fragile than in
appears. When you finally replace the adjuster, don't make the lock nut too

The Modern Bajaj Chetak Rides On The Modern Bajaj Chetak Rides On