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Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level)

152K views 144 replies 18 participants last post by  lt1silverhawk 
#1 ·
**If anything is mislabeled or the information is incorrect, please let me know! Thanks!


- Background -

I have a '77 Chevy pickup that became victim to water and debris in the gas tank (you can read up on that story here.)

At this point, due to the debris getting in the carburetor, it has to be rebuilt.

This is my first time rebuilding a carburetor as well as taking apart and putting together anything on a large scale.

The posts in this thread will be written in such a way as to provide a complete step-by-step documentation of everything I do (aka, sorry if this seems lengthy). This is for two reasons: 1) the other forum members who help out have all necessary information available and, 2) anyone of similar mechanical apptitude as me (which is very minimal) who finds this will be able to follow along without getting lost or intimidated.




- Research -

I began by searching all over the internet as well as local libraries for any guides that can walk me through this process.


I started by decoding the carburetor so I could purchase the proper repair kit. For Rochester, I used the following website: http://www.holisticpage.com/camaro/parts/carb.htm.


The code on this carburetor is 17057525 APP 3356. Based on the information provided by the website the carburetor is:
170 – Built: 1975 and onward by the Rochester Division of GM
5 – Decade produced: 1976 - 1979
7 – Year produced: 1977
5 – Model: Quadrajet (4bbl) California Standards
2 – Division: Chevrolet
5 – Transmission: manual (truck is an automatic)
APP- Customer code
3356- Build date code


With this information decoded, I moved onto to looking for guides on rebuilding these carburetors. Amazon carries a few titles on Rochester carburetors, but the most highly reviewed is “How to Rebuild and Modify Rochester Quadrajet carburetors” by Cliff Ruggles. It was also recommended by another forum member in another thread.


Aside from the book, I also found a couple of forums and websites where a rebuild had been documented. I found this one to be the most informative: http://www.vetteprojects.com/kstyer/quadrajet.htm


Another resource that may prove helpful is the original Delco manual that was uploaded online: http://www.tocmp.com/manuals/Carbs/Rochester/QJet/


Lastly, the one place that everyone can go to learn how to do practically anything is Youtube. Again, a few people took the time to create several videos to show how to rebuild a Rochester carburetor. Due to videos being constantly removed or updated, its best to go look for the newest materials.




- Removal -

The carburetor's removal comprised of the following steps:
1. Take pictures of the carburetor from every angle as it sits.
2. Label all hoses and connections to be removed. In this case, used masking tape since its easy to write on it.
3. Take pictures from every angle of the hoses as labeled.
4. Unbolt the carburetor and remove all hoses and connections (throttle cable, springs).
5. Remove the carburetor and take close-ups shots of everything.




Step 1:





Steps 2 and 3:





Step 5:










- Rebuild Kit -

I purchased a Hygrade brand rebuild kit and float. As warned in the other thread, the instructions do leave much to be desired.

 
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#127 · (Edited)
kikkegek said:
Hi, I want to change my setup to the better setup, but I am looking for people and pictures that already did this on a Quadrajet.

HEre's some pics of mine.
No photos showed in your post.

While the "Best" set up shown above may well be the best, the "Better" image shows a set up that is (IMO) 90% as good as the Best set up. It's easier to do, and only requires that the return springs be attached forward of the throttle cable/linkage attachment point.

Always use a dual return spring- a "spring inside a spring" as used by many OEM's is an excellent type of return spring to use.

Below is a simple $9.00 spring and bracket sold by Mr. Gasket (P/N 720-19) that might work in your situation, and shows the type of spring to use:

 
#129 ·
kikkegek said:
oops, sorry here the pics.
Actually, the way you have it- while crude- is actually not too bad as far as wear on the throttle shaft goes. That said, it's "unsanitary" appearing and the one spring behind the throttle shaft offsets some of the advantage of the forward-mounted spring. Not to mention using the hose to mount the spring- you need to use a solid mounting point rather than tie wrapping the return spring to the hose.

I would suggest you mount a bracket forward of the shaft as shown above and use the dual spring. You will need to improvise how the bracket is made and mounted, to have the spring in line w/the throttle cable (not at an angle, like if the spring were mounted to a small bracket attached to an intake mounting bolt) so the pull of the spring is in the same plane as the pull of the throttle cable.
 
#130 ·
Glad you asked about this kikkegek. I've wondering about how to set this up myself.




cobalt327 said:
No photos showed in your post.

While the "Best" set up shown above may well be the best, the "Better" image shows a set up that is (IMO) 90% as good as the Best set up. It's easier to do, and only requires that the return springs be attached forward of the throttle cable/linkage attachment point.

Always use a dual return spring- a "spring inside a spring" as used by many OEM's is an excellent type of return spring to use.

Below is a simple $9.00 spring and bracket sold by Mr. Gasket (P/N 720-19) that might work in your situation, and shows the type of spring to use:

Hey cobalt327,

Does the bracket mount in a specific place or does a hole have to be drilled in a specific place to install it? Or if that's too much work, would the setup pictured below be a better choice? It is a manifold-mount universal set up (attached are the installation instructions in pdf). I couldn't find one that was Q-Jet specific on Summit.

 

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#132 ·
kikkegek said:
I made a custom bracket myself tonight and mounted it to the brakcet of my A/C pump. The springs are still not puling hard enough for my setup. I will have to fine tune it. I'll takes some pics tomorrow.
To add to the information. It seems that only when the engine is warmed up, I have the high idle problem, because the throttle linkage last bit has extra resistance. So the last 1-2 mm before it hits the idle screw feels heavy. So heavy when warm, that the springs dont pull it back to full idle, making it idle at about 1000-1100 rpm.
 
#133 ·
heavy throttle

check the throttle shaft bushings for wear. that is common problem. the throttle shafts bind because the butterfly valves never end up in the same place twice. thery also leak vacuum so it is hard to adjust the idle mixture. also check all the rest of the linkages and pull offs on the carb. some are affected by the choke so if the choke is still on a little that part of the linkage isn't operative. like the 4bbl lockout won't owrk if the choke is active. grab some carb cleaner/lubricant spray at the parts store and do a little clean up of all the rods etc. if you have a little extra cashola, get a new aftermarket carb and some new distributor weights and springs (recurve the distributor) at the same time. that will perk it up. have to spend a couple hundred though.
good luck,
dsraven
 
#134 ·
OK,

heres some pics of my forward "better" spring setup. Its hard to take pics, but here they are.

I noticed that in my setup my spring was about half an inch shorter stretched in "idle" position then in the carbs original setup.

So today I drilled two more holes too stretch it a little more. I'll take a drive tonight and report back on it.




 
#136 ·
lt1silverhawk said:
Hey kikkegek,

That looks pretty good. Where did you mount the bracket to?
I mounted it to on of the big screws of the A/C bracket.

I didnt help me sofar though. I still have high idle. I did notice that with the engine warm and not running the linkage runs smooth and free. When I turn on the engine and it is warm...the last bit of the linkage...1-2mm is not smooth...

I checked if the fast idle cam is keeping the idle high, but it isnt...what else can it be?
 
#137 ·
kikkegek said:
I mounted it to on of the big screws of the A/C bracket.

I didnt help me sofar though. I still have high idle. I did notice that with the engine warm and not running the linkage runs smooth and free. When I turn on the engine and it is warm...the last bit of the linkage...1-2mm is not smooth...

I checked if the fast idle cam is keeping the idle high, but it isnt...what else can it be?
While I don't know the answer to your question, I'm bumping this post up so hopefully someone responds soon. If it is possible, can you make and post a video showing what happens? Maybe two videos, one with engine on and the other with engine off?
 
#139 ·
alrighty,

checked the choke unloader. unplugged it...first put a hose on it and sucked on it, but the unloader doesnt move...

I then plugged the connection to the carb and drove it a bit. But no change.

Still got the annoying high idle when I dont kick the throttle...

I made two short films (As requested) hope you guys can see what I mean...

first one without engine running (sorry movie is upsidedown)
http://www.youtube.com/watch?v=lAIkJiofIAA

second one with engine running (sorry again upsidedown)
http://www.youtube.com/watch?v=3ZKK1kIdVZ4

As you can see it is only a very little bit that the throttle stays open.

and it's almost like the little play there is in the linkage seems to be gone when the engine is running. I can not feel any play when the engine is running.
 
#140 ·
Hey kikkegek,
kikkegek said:
alrighty,

checked the choke unloader. unplugged it...first put a hose on it and sucked on it, but the unloader doesnt move...

I then plugged the connection to the carb and drove it a bit. But no change.
Are you referring to the choke pull off? See the picture attached for the part I am referring to.


kikkegek said:
Still got the annoying high idle when I dont kick the throttle...

I made two short films (As requested) hope you guys can see what I mean...

first one without engine running (sorry movie is upsidedown)
http://www.youtube.com/watch?v=lAIkJiofIAA

second one with engine running (sorry again upsidedown)
http://www.youtube.com/watch?v=3ZKK1kIdVZ4

As you can see it is only a very little bit that the throttle stays open.

and it's almost like the little play there is in the linkage seems to be gone when the engine is running. I can not feel any play when the engine is running.
I really couldn't hear the engine over the wind noise, but Im sure the experts on this forum will come through. Btw, did you consider trying the single or double-spring set up that cobalt327 and Willys36 posted pictures of (posts 127 and 138)?
 

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#141 ·
yes I mean the choke pull off. I unhooked it, tested it, sucked on a hose and it didnt do nothing. what does this thing do and how can it keep my linkage from going to normal (low) idle?

and as for the linkage setup .I have it setup just like that now with a double spring. Check this picture out:



so I am really in the dark why I ca fix the high idle problem.
 
#143 · (Edited)
lt1silverhawk said:
That looks like a nice setup.

About the choke pull-off, according to "How to Rebuild and Modify Rochester Quadrajet Carburetors", Ruggles says to "vacuum-test the factory choke pull-off and replace as needed." (page 87). If sucking on it isn't working, it might be time to replace it. (Damaged diaphragm?)
okay, thanks for that. But in my setup, I dont need the choke. My engine will start however cold it is, because I run LPG for main fuell and only have regular fuel for backup.

So I will only repair the pull off if it is causing the high idle. And as far as I know, it has no relationship to that. Or does it?

@Willy, thanks for the nice and clear picture. Looks nice and clean!
 
#144 ·
The choke pull off needs replacing regardless of the idle situation. It controls the opening rate of the secondary air valve. It applies force when it has vacuum applied (like at idle :mwink: ) to the air valve linkage that holds the air valve and everything else attached to it (this depends on the exact carb in question as to what else, if anything, is included) in the proper position.
 
#145 · (Edited)
I wanted to give some updates on the carburetor since the rebuild.




First off, all of the information on this thread was compiled and properly organized into this wiki: "How to rebuild a Rochester Quadrajet 4MV carburetor". A few members have added additional info to what is found in this thread, so please do check it out.




During the rebuild, I did dab 5-minute epoxy over the plug wells as a precautionary measure. The carb was recently disassembled for a clean up, and the epoxy had corroded and had become flaky. It was cleaned off. The wells don't seem to be leaking.






It was noticed during this past dis-assembly that the main well bleed tubes in the air horn were clogged. They were cleaned out using Hobart 770085 Welding Oxy-Acetylene Tip Cleaner. The procedure involves dissembling the top end of the carb, finding the largest tip cleaner that fits inside the bleed tube, and slowly filing away. Keep moving a size up until its all cleaned out.







Another thing that was missed during the first rebuild was the eccentric plastic cam in the air horn that is responsible for the secondary metering rods. It was found during a recent reassembly in the float bowl body, where the key that operates the choke plate is found. The part was ordered from Cliff Ruggles' site. The kit also included new screws for the air flaps.


The procedure replacing the cam involves removing the air flaps and shaft assembly, and is outlined in the images below.


 

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