Author Topic: Idle specs for 1978 Rochester quadrajet  (Read 610 times)

Offline MY1978

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Idle specs for 1978 Rochester quadrajet
« on: August 20, 2023, 07:47:02 AM »
Can someone please provide me with the idle specs for a Rochester 4bbl quadrajet.  When i start it when cold it wants to stall out several times unless I push the accelator pedal to rev back up.  After it starts warming up it will ramp up to high idle and then after the given warm up time (which seems like forever based on today's vehicles) it will idle down to mid and then low with a kick down.

So, can someone tell me what the idle speed(s) should be please.  I have someone that is coming over today to work on it.

Thanks


Offline zieg85

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Re: Idle specs for 1978 Rochester quadrajet
« Reply #1 on: August 20, 2023, 08:39:23 AM »
There is a lot of information on the web if you google it.  From your description it sounds to me like your choke pull-off isn't adjusted right.
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
https://www.facebook.com/groups/248658382003506/

Offline Mr Diesel

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Re: Idle specs for 1978 Rochester quadrajet
« Reply #2 on: August 20, 2023, 10:43:59 AM »
#1. Don't ever compare a 1970s or 1980s carbureted vehicle to a modern vehicle. There is no comparison and they will never be comparable. These old vehicles usually warm up a lot slower than a modern vehicle at idle. The fastest way to warm up an engine is to drive it.

#2. Set the idle speeds at whatever suits you and the driveability. Generally I like my warm idle set around 700rpm and cold high idle 1,000-1,200. It doesn't matter what any manual or spec sheet says is "right" for it.
1976 C20 Crewcab, 6.2L/SM465
1982 K30 Crewcab , 427TD/TH400
1983 C30, 6.2L/TH400
1983 K30 Crewcab 454/700R4
1986 K10 350/400. 1989 K30 cab/chassis 454/SM465

Offline JohnnyPopper

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Re: Idle specs for 1978 Rochester quadrajet
« Reply #3 on: August 20, 2023, 04:26:57 PM »
I read thru the thread a couple of times, did someone make a comparison?  ;D

Unless you have a manual choke (if you dont have a cable to pull, it's not manual) your carb operates with a single pump before starting. Not a light pump, push at least half way.

If your engine/carb is cold, a properly adjusted choke will engage to the degree needed. After the warmup, the the kick down you speak of will bring down to the low idle.

Check out this info. https://www.youtube.com/watch?v=_BTEdWt2V3s&t=103s

Which one are you?
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline zieg85

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Re: Idle specs for 1978 Rochester quadrajet
« Reply #4 on: August 20, 2023, 11:14:15 PM »
I read thru the thread a couple of times, did someone make a comparison?  ;D

Unless you have a manual choke (if you dont have a cable to pull, it's not manual) your carb operates with a single pump before starting. Not a light pump, push at least half way.

If your engine/carb is cold, a properly adjusted choke will engage to the degree needed. After the warmup, the the kick down you speak of will bring down to the low idle.

Check out this info. https://www.youtube.com/watch?v=_BTEdWt2V3s&t=103s

Which one are you?

This is what is out of adjustment and what is called a choke pull-off
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
https://www.facebook.com/groups/248658382003506/

Offline JohnnyPopper

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Re: Idle specs for 1978 Rochester quadrajet
« Reply #5 on: August 22, 2023, 10:52:39 PM »
WOW look at all that metal!!!

That's another comparison to modern day cars, so much are synthetic.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction