I've removed throttle body (my sweaty work!....hehe.), found carbon deposits on throttle valves (while the sub-throttle valves in the upper side looks clean) and bad deposits in throttle neck & intake valves of the engine, carbon formed like gum or glue. I cleaned throttle body with petroleum based cleaner, lubricate throttle cable. It shows better moves right now.......but I'm not sure problem fixed or not. My throttle grip gets sticky after sitting overnight,......let's see how it go tomorrow!
What does the inside of the airbox look like, specifically the rear-side where the crankcase breather hose connects? Excessive oily vapor from the crankcase can cause deposits inside the intake tract.
re Bad deposits on the intake valves: Did you get a photo? Such deposits can be a sign of valve seal issues or loose valve guides allowing excessive oil down the stems where they collect and gum up on the backs of the intake valves. If you're not doing so now you might consider using a high quality full-synthetic oil with a viscosity one point higher than you're running now (as long as you don't go higher than the manual calls for...)
It's very strange to have a sticky throttle control. You should try to isolate where the stickiness is occurring. Is it at the throttle bodies themselves, in the cables or the throttle tube on the handlebar.
How did you lube the throttle cables? If you don't have one already consider investing in a proper cable luber:
It ensures that lube gets all the way down the jacket sheathing so the whole length of the cable is lubed, not just the part you can see.
unfortunately, I did not remove intake hoses from crankcase so could not take good pictures of them however I did see (using torch) black gum stuck on track, on intake valves face & stem, fuel passage holes & throttle valves face. I am using fully synthesis oil SAE10W-40 (brand DP Racing oil) for the bike, it's quite hot & high humidity in my country (Viet Nam), "Excessive oily vapor from the crankcase" which you mean caused by lub oil?
- I can confirm throttle bodies had sticky after I removed cables and turned it by finger, it was hardly to open & slowly return by springs
-Yep, throttle cable lubrication also a problem in my case, I just can do it drip by drip and .......hope lube goes along with cable down to the other side of jacket sheathing. I'll buy one luber.