I don't understand the "hanging off it like a flag" part. And I have no idea if the throttle slide (throttle valve?) is sticking or not. Prior to all this I had the same high rev issue. I took the throttle valve out and sanded it smooth with very fine grit sand paper, lubed it and put it back in. I checked and it was going up and down nicely. Could I have the throttle cable adjusted so badly that it's causing these high revs? I set it by the manual.

Just meant if throttle is stuck open & push starting it'd take off with you hanging off the side of it not being able to jump on.

So long as the slide is hitting the bottom with idle speed screw backed out & you have clearance on the cable when slide is down it should be ok, then can bring the idle up on the speed screw to whatever idle speed you desire. I'm wondering if there's something very unusual going on.

When you open and close the throttle can you hear and feel the slide going up and down? Sounds similar to a problem I had where the slide would stick if the carb was tightened normally. Backing off the torque on the nuts would allow the slide to move normally. Others on the forum noted my case was caused by a warped flange and/or incorrectly sized o ring that sealed the carb to the reed block.

Throttle is stuck or you have an air leak. 

I learned long ago to twist the throttle and check for the sound/feel "thunk" of the slide closing before attempting to start.  If slide is closing and stop screw is backed off, must be an air leak.

Sorry, RT325; just read that flag comment wrong, I guess. Now that I re-read it, it makes sense.

Okay, been a long time, I know. Took a trip to England with the family. Loved it! Want to move there! The Brits are so nice!

Anyway, I tore some things apart and took these photos: They were taken from the reflection of a mirror, so I know they are distorted, not a warped carb mouth.

The first photo is with the throttle cable attached and the throttle valve is sitting half-way (or all the way?) open. Revving the throttle with the cable attached only makes the throttle valve open up more. It never goes all the way down.

flic.kr/p/2pYkPs6

The second photo is with the throttle cable disconnected and the throttle valve is closed, all the way down.

flic.kr/p/2pYkPNM

So, what this seems to tell me is I have a pinched throttle cable somewhere, yes?

Here is my cable routing/layout. I don't see that I'm doing anything wrong.

flic.kr/p/2pYkomh

Where did you get the cables and connecting tube from?

It's been a while now since I fitted mine, but the pattern cable set that came with my project RT2 had instructions that, for some models, the outer sheath for the carb cable had to be reduced by 10mm. When I first fitted my cable, before alteration, the throttle valve was left hanging like yours.

I got my bike shop to loosen off the ferrule in order to push it off the outer sheath, carefully cut away the 10mm of the sheath, and then crimp the ferrule back onto the sheath.

Oh, and how dare you call us Brits nice! 

"Pinched" cable would mean something like throttle would pull the slide up but the friction in the cable would be too much for the spring to push the slide back down.

I agree with Allan, seems like you have the wrong cable, cable assembled incorrectly, or somehow not enough slack adjustment to allow the slide to drop down.