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1966 Rochester idle

Started by dgll411, May 18, 2023, 05:40:58 PM

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dgll411

Hello, I just had my carburetor rebuilt. Now it idles to high. Where is the idle adjustment screw? I am used to seeing it by the accelerator cable, but its not there.

Julien Abrahams

On my '67 there is no accelerator cable, but three accelerator linkages. There should be a linkage that rests against the idle adjustment screw on the driver's side of the carb.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

35-709

#2
'67 is different with a Q-Jet, '66 was the last year for the Carter AFB or Rochester 4GC, both were used.  I am not familiar with the 4GC
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

signart

#3
Here you go, Cadillac Rochester 4gc.
You might have to open throttle to see, look under linkage.  Passing gear switch installed on yours may be obstructing your view.  It is not installed on this carb.

Rochester idle adjust.JPG
Art D. Woody

dgll411

The image in the last post is the fast idle screw if I'm not mistaken.  I found a piece that looks like a vacuum actuator that screws in and out. This piece seems to control the curb idle.

Caddyholic

I think the idle is adjusted with the air adjustment screw on the back of the 4jet.
I got myself a Cadillac but I can't afford the gasoline (AC/DC Down Payment Blues)

1961 Series 62 Convertible Coupe http://bit.ly/1RCYsVZ
1962 Coupe Deville

Carfreak

Enjoy life - it has an expiration date.

dgll411

This seems to be the adjuster.

jcat

wouldn't it make more sense that the vacuum actuator looking thing would be the fast idle adjuster?  it's spring loaded, you can push that plunger in regardless of bolt position.  Car fast idles on cold start then gradually winds down as it either a.) builds vacuum or b.) temperature?

I haven't gotten my corrupted shop manual PDF fixed yet...otherwise I'd check that.
Joe Catanzaro
----------------
1969 Sedan Deville
2017 S550 4matic (daily)
2017 XC90 T6 (wife's ride)
2015 F-Type R
2004 F350 5.4 (work pig)
2004 Grand Marquis

Ralph Messina CLC 4937

Dan,

 There's a large screw at the lower rear driver's side corner of the carb. It is the idle By-pass screw and controls the idle after the engine warms up and the high speed idle is off. When is the idle too high?.

 I'm not certain from the first pic in Signart's post but that location looks like the highspeed idle control screw. That screw comes into play when starting cold and a quick stab on the accelerator will knock the fast idle off. Working with the idle by-pass screw, note the clock position and rotate it ¼ right and left to see which way it effects the idle speed. Do this with the engine fully warmed up. If the problem is only when starting cold, the high speed idle screw needs adjustment. That location is difficult to access.

 Editorial note: The Rochester and Carter carbs used interchangeably in '66 are supposed to provide the same performance, but the Rochester is twice as complicated and a RPIA. IMHO the design was was revenge by some engineer who was secretly a Ford or Mopar guy.

HTH
1966 Fleetwood Brougham-with a new caretaker http://bit.ly/1GCn8I4
1966 Eldorado-with a new caretaker  http://bit.ly/1OrxLoY
2018 GMC Yukon

dgll411

Quote from: jcat on May 23, 2023, 09:34:23 AMwouldn't it make more sense that the vacuum actuator looking thing would be the fast idle adjuster?  it's spring loaded, you can push that plunger in regardless of bolt position.  Car fast idles on cold start then gradually winds down as it either a.) builds vacuum or b.) temperature?

I haven't gotten my corrupted shop manual PDF fixed yet...otherwise I'd check that.

It would first appear that way, but the piece has no connections and screws up or
Down adjusting the idle speed. Not sure if that is its purpose,  but
thats what its doing now. Maybe its a cushion for the lever if it snaps back quickly.

Daryl Chesterman

Maybe its a cushion for the lever if it snaps back quickly.  That is correct Danny.  Read these two websites for more insight into the dashpot, that you are talking about—it is NOT used to adjust the idle speed.

     https://www.carburetor-blog.com/carburetor-dashpot/

     https://www.timesmojo.com/what-is-the-purpose-of-a-dashpot/

I think the idle is adjusted with the air adjustment screw on the back of the 4jet.

I think Caddyholic is correct—you can see the adjusting screw (that has the spring around it) at the left-rear of the carburetor, beside the mounting bolt in the picture from your post #7.


Daryl Chesterman

jcat

Interesting. Logical use and makes a lot of sense!  So crazy the solutions they came up with before computers controlled everything. 
Joe Catanzaro
----------------
1969 Sedan Deville
2017 S550 4matic (daily)
2017 XC90 T6 (wife's ride)
2015 F-Type R
2004 F350 5.4 (work pig)
2004 Grand Marquis