When you open up the twistgrip, what the picture Brien's posted doesn't show is the friction spring and adjusting screw that might be present in the twistgrip mounting (parts 4 and 5 that Brien's marked in yellow in the picture he's posted).
The friction 'spring' is a piece of copper-coloured strip bent into an arc matching the larger diameter of the twistgrip drum (part 9); if it's present, ime it needs very little pressure from the adjusting screw to apply friction to the drum. To ensure
that it isn't applying any pressure, I set the adjuster screw and locknut before
I assemble parts 4 and 5.
If the friction spring adjuster screw appears to be present, another thing to check is it's the correct one; the screw and locknut drop out if the nut comes loose then they're replaced by any old screw that fits.
The correct screw has a short length of small diameter without thread - that fits in the hole in the middle of the friction spring.
As I say, I set the adjuster screw and locknut before I assemble parts 4 and 5. I fit the adjuster screw (in part 5) so that just
the length without thread is visible inside - to locate the friction spring; obviously, I secure the screw in that position with the locknut.
Btw, because parts 4 and 5 have space for the friction spring, and the cable attachment area on part 9 to rotate, it doesn't matter that 4/5 don't have any grease; nothing of part 9 should contact anywhere on parts 4 or 5 when the former rotates. The only exceptions are:-
. if a 'twistgrip travel limit adjustment screw' (also not shown in Brien's picture) is present; the end of the cable attachment area on part 9 contacts the end of screw if it's present;
. if the screw isn't present, the end of the cable attachment area on part 9 might
contact part 4 at the limit of the twistgrip's rotation if the carb. slides don't reach their limit first.
So, during most of the twistgrip's rotation, nothing of part 9 should
contact anywhere on parts 4 or 5. However, they're three separate parts so imho it's as well to actually check this during assembly - I rotate the twistgrip every now-and-then as I tighten the two screws (10) that clamp parts 4 and 5 together. When parts 4 and 5 are completely clamped together:-
. if the carb. slides are attached to the other end of the throttle cable, the twistgrip should rotate open easily and snap shut when it's released;
. if the carb. slides aren't attached to the other end of the throttle cable, the twistgrip should rotate easily both ways held only between thumb and forefinger.
Ime, there are also two other places on the twistgrip assembly that can cause drag:-
. because parts 4, 5 and 9 are three separate parts, 4 and 5 allow for a little movement along the handlebar by 9; this can allow the fitted rubber (part 11) to drag against 4 and 5;
. the other end of the rubber 11 can drag on the end of the 'bar;
... if, when you assemble parts 4 and 5 around 9, you're feeling some friction and you're certain nothing on 4/5 is rubbing on 9, try pulling the whole twistgrip a little towards the end of the 'bar.
Finally, I agree with "750 Tracker" about grease (or oil) between the drum and the 'bar; I'd use either the teflon spray, or I've also used the cheap spray-on furniture polish I keep in the garage for fitting and cleaning rubber parts.