Low idle Quadrajet

[48bill]

I can't get the idle below 1100 rpm on the quadrajet.  The idle screw is backed out and it isn't touching the stop.

It is on a 425 ci 1978 Caddy engine.  There is no choke and the high idle screw is also backed all the way out.

Suggestions???

Thanks.

[wayne petty]

are the secondary throttle blades closing fully???/  i have found them slightly out of alignment.. and also held open with debris..

some cad carbs have a hot idle compensator #37... bimetalic spring device under a vertical cover #36 on the center back of the main body..  2 small screws to hold the cover on.  #35.. and some kind of seal there also #38


the little assys are usually held in with a single screw.. under the cover...


i also take it that the primary throttle is off the fast idle cam... passenger side of the carb...   OHH!! i seen you already answered that..


here is one of the many articles on that carb..

http://www.hemmings.com/mus/stories/2007/05/01/hmn_feature20.html

one thing... if you have to take the carb apart... DO NOT remove or adjust the lean limit screw in the main body..  it is between the needle and seat and the power valve piston bore..  it takes a pair of needle nose or a double D screw driver to turn it..  do not adjust it... if you have post.. there are tricks to get it properly readjusted..  it effects power, fuel economy, emissions,  drivability...

[reborn55]

Disconnect the throttle linkage and see what happens.

[chimp koose]

What is your timing set at? If its got way too much initial timing it may cause a high idle. Are your idle mixture screws turned way out? Ive seen some that were out so far as to cause a vacuum leak.

[48bill]

Thanks reborn55 that was the solution.  The throttle cable had shrunk?.

I will keep the other info for when I need to rebuild the carb.