I was cruising around and I hit this thread and the following passage caught my eye....

What is this coasting valve thingy that he speaks of? My idle has been the idle from hell, and it too dies at stop signs sometimes. Also, MMO will help my idle? I plan on doing a dizzy tune up on my 85 GS... new rotor/cap etc etc. If that doesn't help though, I wanna get this valve looked at... or pulled out, whatever. Suggestions?

 

It's a second butterfly under the primary for the rear rotor. Apparently, it draws vacuum and closes during deceleration for some dumb reason. I think the reason it causes problems with idle is that it creates an irratic vacuum pull (just a guess.) What sucks is that I had the whole intake off the car, and I actually tried to remove the thing. I stopped when I couldn't break the screws loose without marring them. Then I actually repaired it the linkage that was getting worn out. Then I looked a the forum, and found out that I should have just clipped the damn thing out with dikes.

Anyhow, that's what I know.

 

Not sure where the coasting valve is, if there even is such a thing, unless I'm wrong, what cheapie is descirbing is the shutter valve, and I believe thats what the person who posted that original quote probably meant the same thing.

 

There is a coasting valve. It's located on the driver side of the carb below the blue canister. It's got one small hose that goes up the the air canister near the big hose for the shutter valve.

 

Oh... well, I was talking about the shutter valve. Sorry for the confusion.

 

That shutter valve is disasterous.

(shutter valve)

 

Thinking about it still makes me shutter.

 

On decel, the valve closes, forcing the air fuel mixture from both carb primarys into the front rotor, and just air to the rear rotor. This lowers the misfire rate for the front rotor, which lowers emissions and keeps the cat temp from getting too high.