Quote:
Originally posted by ianc
There isn't an upper decel, there is only the decel valve. This is the flying saucer shaped thingie with the vacuum connection. It is supposed to slow the engine's mad dash for idle when you lift off the throttle suddenly to prevent a lot of unburnt gas from hitting the exhaust. Disconnecting the vacuum line from it will often make it shift easier, so people do. I did.
Under high manifold vacuum it allows more air to bypass the throttle to create a more combustible mixture until the engine slows to idle. If you're getting an increased idle when you connect it, the diaphragm inside it is probably leaking. Vacuum leak, in other words, and this could be the source of your problem. Remove it and check.
ianc
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I swear I have two flying saucers, one right above the other, I'll try and get a pic. Each is identicle and each has a vacuum nipple. They are also both part of the same system, I remember this when I had the motor out and had to remove the hard line to replace the breather gasket.