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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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#52 ·
**CORRECTIONS**

I obviously misread the section quoted below. cobalt327, you were talking about the tubes in the airhorn. The books does not offer a procedure for removing them.

cobalt327 said:
In any event, this means removing the down tubes from the airhorn (unless, God forbid, you want to sand on the main body :sweat: ). Measure their installed height before removing them, and be careful when you remove them.

I don't know what procedure he uses for this. If you would, post what it is. I would insert a solid piece of wire the same size as the ID of the tubes into them so they could be gripped w/o crushing them.

The inner tubes are bottlenecked on the bottom, so you will want to go in from the top w/the wire "reinforcement", should you try to remove them this way. The inners are also small, it may take a bit from a numbered set to do it, or maybe a cut down pin, etc. Make sure the end of the wire extends out of the tubes, after gripping them for removal the wire will be trapped and you'll want to be able to grip the wire for removal.
Also, I did not give due due credit in the last post for the quotes so here it is: **All quotes and cited sections are from Cliff Ruggles' "How to Rebuild and Modify Rochester Quadrajet Carburetors", copyright 2006.


No more reading technical stuff while sick with the flu. Lesson learned. :embarrass




---------------




In the book, Ruggles really stresses installation of primary shaft bushings:
"A must for all rebuilt Quadrajets, installing primary shaft bushings reduces side play at the primary shaft. Leakage at the primary shaft is a big problem with used carburetors. It not only makes tuning nearly impossible, but it also allows unfiltered air to enter the engine. A custom self-guiding drill bit is used to open up the shaft bore in the base plate. A bronze bushing coating with Red Loctite is then driven in place." (chapter 5, page 73).
This bushing kit is available on his website for $59.95 + $6.50 S/H as of this writing.

I unfortunately do not know if my carburetor is suffering from any leakage. But regardless, is this a worthwhile procedure, especially considering the cost? I hope to talk to Ruggles about this over the phone once I am better, but I was curious as to what others have to say.




**All quotes and cited sections are from Cliff Ruggles' "How to Rebuild and Modify Rochester Quadrajet Carburetors", copyright 2006.
 
#53 ·
The primary bushing kit is another mod that I put into the "only if another base plate cannot be found or it's rare carb" category. For that much money, a guy could prolly find two or three cores that need nothing done to the primary throttle bores. Now, if cost isn't a primary consideration, for sure go ahead and do it. Hell, RPD should have installed bushings from the get-go, IMHO. Secondary shaft wear hasn't been an issue w/any of the carbs I've seen.

Whether or not the wear is going to cause idle problems (at speeds above an idle, the shaft play is not a consideration) depends on just how significant the wear actually is. This can be judged by if the primary blade on the throttle linkage (left) side of the carb can touch the throttle bore, and/or by how well the carb will hold a steady idle, w/o it 'hunting' or being erratic.

A lot depends on how the return spring was set up. If the spring pulled rearward (same direction that the throttle cable pulls) from the lower part of the throttle arm, wear can occur within the life of the engine it was installed on because both the throttle linkage AND the spring is working together to cause twice the wear. But if the return spring was hooked to the upper throttle arm and was attached to a bracket forward of the carb, this will act to offset each other and the wear will be less.

As far as milling the main body, the boosters are above the plane of the gasket surface and they are not removable. So milling the body would be a machine shop-type op, as far as I'm concerned- I cannot envision doing this on a belt sander w/any real hope of success. In any event, it's going to be the airhorn that's warped in the majority of cases, anyway.
 
#54 ·
cobalt327 said:
A lot depends on how the return spring was set up. If the spring pulled rearward (same direction that the throttle cable pulls) from the lower part of the throttle arm, wear can occur within the life of the engine it was installed on because both the throttle linkage AND the spring is working together to cause twice the wear. But if the return spring was hooked to the upper throttle arm and was attached to a bracket forward of the carb, this will act to offset each other and the wear will be less.
Going by the pictures of the carb as it sat in the truck, the springs are setup for a forward pull and seem to be in good condition.




--------------------




Last week, I called up Ruggles and ordered the parts from him. Very nice guy to talk to and, of course informative. I asked him about some of the discrepancies between my carb and what is provided in the decoding info. Ruggles said that the divorced choke carbs were used on the trucks until 1978, that's why some of the parts are listed for older models.

I went ahead ordered the power piston retainer, the ros retaining clip and the accelerator pump. The parts showed up by Thursday.

 
#58 ·
emazingli said:
That's nice lt1silverhawk! Good progress of your project. More luck for it. ;)
Thank you! I really appreciate your encouragement. :D




silentpoet said:
you take very good pictures. Better than the ones I took of my carb.
Thanks! The tip about taking good pictures was given early on so I am making sure to that. Plus, a few minutes on the photo editor (Photoscape) to brighten, crop and combine helps alot too. :thumbup:
 
#59 ·
- Power Piston Retainer and Rod Retainer Clip Installation -

I finally tackled the power piston retainer and rod retainer clip today, which arrived last week. The rod retainer was fairly easy but the piston retainer was not a perfect fit right out of the bag. First, I had to break the old retainer. After I slipped on the new "split" type, I found that it was just a bit too large. After failing to cut off a piece of it with a knife, I ended up sanding down one side of the opening until it was perfect fit. Might even be a bit too snug.

 
#60 ·
lt1silverhawk said:
After failing to cut off a piece of it with a knife, I ended up sanding down one side of the opening until it was perfect fit. Might even be a bit too snug.
Just be sure that when it's all said and done that there's positively no friction from the retainer on the PP shaft itself. It has to be absolutely free to move w/o any hindrance.

The throttle blade correction looks spot-on. I like the "patriotic" look of the retainer and accelerator pump piston assembly! But seriously, those are said to be among the best available.
 
#62 ·
Hey cobalt,
cobalt327 said:
Just be sure that when it's all said and done that there's positively no friction from the retainer on the PP shaft itself. It has to be absolutely free to move w/o any hindrance.
I tested it out and the PP is popping up with no hindrance. I was more concerned about the air horn gasket getting in the way but no issues yet.



cobalt327 said:
The throttle blade correction looks spot-on.
Sweet! Wasn't very hard to do either. But definitely requires care and patience.




cobalt327 said:
I like the "patriotic" look of the retainer and accelerator pump piston assembly! But seriously, those are said to be among the best available.
Lol! That's a good catch! I never even paid attention to the color combo. Its good to know the parts have an excellent rep.




----------------------




Hey Willys36,
willys36@aol.com said:
Trottle spring orientation is critical to the life of your primary shaft bushings as mentioned above for any carb installation. Design yours like the 'best' picture below and your shaft busings will last forever.

Thanks for the diagrams. :thumbup: These are very helpful. Comparing them to the pictures of my truck's setup before the carb was removed, the throttle spring
was setup as Bad. My question is how does one improve this setup, i.e. how do I go about adding a bellcrank (best) or attaching the spring ion the oppostie direction of the throttle force (better)?






Thanks for the continued help and input folks! :thumbup:
 
#63 ·
**Note** I wanted to mention the fact the gasket between the float bowl and the air horn has to be slipped into place once the float, needle and power piston are in place. The procedure is covered in this video at 3:20.




-------



I hit another bump in the road today. Despite my best efforts at photographing everything from every angle possible, I apparently didn't do a very good job of photographing the choke (linkage?) setup. I did a test fit this morning. Does it look right? Any help in this matter is greatly appreciated. Feel free to copy and edit pictures. I can post the original pictures before disassembly for comparison if needed.


 
#64 ·
cobalt327 said:
Just be sure that when it's all said and done that there's positively no friction from the retainer on the PP shaft itself. It has to be absolutely free to move w/o any hindrance.
For the visual folks, here is a quick 8-second video showing how the power piston is moving after installing it with a new retainer, along with the gasket between the float bowl and air horn.




--------------------------




I continued with the reassembly of the choke setup. I used the pictures I had taken before disassembly, along with the pictures found on this page by 4wheelnoffroad.com. While searching for good pictures, I realized that not taking pictures from the right angles before dsiassembling is rather common rookie move. Lesson learned.



Feeling confident that I set up up the choke assembly correctly, I went ahead and removed it and tackled what I've come to learn is perhaps the most ... challenging ... part of the reassembly: installing the three-hole "key" and linkage rod from the choke plate to the choke shaft (if any of this terminology is incorrect, please do point it out. I'm sure I just made up some of this stuff). Apparently, "fishing" method works best, although a member on another site was mentioning a tool called "magic fingers", which quite possibly might be this?






Installing this key took forever. And the worst part? Right after I got everything set up, including the airhorn on top, I remembered I had never put in the accelerator pump. Depending on individual patience level and reserves, this could be a blow-up point.

I went ahead and raised the airhorn a little, while also lifting the gasket for some unknown reason. I installed the accelerator pump, and tried tried setting everything back in place. The image seen below has got to be a rebuilder's nightmare. But I did get it all fixed. :D

 
#65 ·
I have a serious concern about the secondary lockout lever. It sits in the "locked out" position with the little tab from the secondary plates shaft. From what I understand, the fast idle cam moves the secondary lockout lever out of the way under full throttle, but is it supposed to sit like this? Any info on this is greatly appreciated.

Just out of curiosity, can the carb work well without a secondary lockout lever?

 
#66 ·
The photo above is the correct position for the lockout- with the choke closed. As long as the choke is closed, the lockout will be in effect. After the choke opens, the lockout will retract, allowing secondary action. So, as long as the choke is correctly assembled, the lockout will work as designed.

The only thing I can see that could be a problem is if the build up of paint prevented the lockout from working w/o any "stiction", being as how carbs aren't usually painted.

A Q-jet will work perfectly fine w/o the lockout- just be sure the engine is warmed up before matting the throttle.
 
#67 ·
Hey cobalt,

cobalt327 said:
The photo above is the correct position for the lockout- with the choke closed. As long as the choke is closed, the lockout will be in effect. After the choke opens, the lockout will retract, allowing secondary action. So, as long as the choke is correctly assembled, the lockout will work as designed.
Understood. I was doing a test of all the linkages and shafts and just became concerned that the lever may not be moving out of the way because of the way I installed the fast idle cam or something. I guess its all the nervous wondering about if I put everything back correctly before I slap it back on. :)




cobalt327 said:
The only thing I can see that could be a problem is if the build up of paint prevented the lockout from working w/o any "stiction", being as how carbs aren't usually painted.
Yeah, the paint job might've been a bit overkill. Its not too late to sand down any parts if there is a case of stiction (cool word, btw).




cobalt327 said:
A Q-jet will work perfectly fine w/o the lockout- just be sure the engine is warmed up before matting the throttle.
Still havent learned how to properly warm up my truck. I drove it so little, before the carb rebuilding came up, that I would just start it once a week for a street cleaning and let it warm up for a good five minutes before moving it up the drive way. The previous owner removed the thermostat so it has always run pretty cold.




Thanks cobalt :thumbup:
 
#68 ·
- Reassembly, cont. -




Bolting It Down
With throttle plate, float bowl, float and airhorn in place, I went ahead and bolted it all down with the 9 bolts: 2 long, 5 medium and 2 small.





Secondary Metering Rods Assembly
The secondary metering rods are installed between the secondary throttle plates. There are two holes behind the choke plate where the rods themselves slip into.The assembly is then held in place by a small bolt.





Accelerator Pump Rod and Lever Assembly
I resued the same dowel pin to hold the lever in place since it was already pretty tight in there.




Fuel Filter Housing Assembly
Pretty straight forward. I did not use a filter on this one because the truck already has two canister type filters along with a glass-cased one right before the carburetor.





---------------------




Anyone know what this part is called and what it does?

 
#69 · (Edited)
The part you were wondering about the name is a "dashpot". It acts as a slight delay, preventing the throttle from 'slamming' shut. It's unnecessary for the most part.
EDIT- I see yours has a vacuum barb on it. This may still be just a dashpot, or an idle speed modulator of some type- I do not recall ever seeing a vacuum barb on a dash pot- so I'm at a bit of a loss as to what it is, exactly.

What action occurs when vacuum is applied to it- does it retract, or ?

EDIT II- You will sometimes hear the choke pull off/unloader or secondary vacuum break called a "dashpot". The dashpot I'm referring to above (that checks the throttle closing) has nada to do w/the choke OR secondary action- just so we're clear on this. Because if you google "q-jet dashpot" (like I just did looking for info on why there'd be a vacuum barb on a dashpot), most of what comes up has to do w/the choke unloader/pull off.

BTW, I saw nothing on a vacuum assisted dash pot, so I'm still at a loss. If I see something on this, I'll post it and you do the same. There were just SO MANY iterations of the Q-jet through the years that keeping up w/all of them is quite impossible- there always seems to be something different.

"Stiction" comes from the motorcycle magazines of the '70's. It was used by to describe the fork seal to fork tube stickiness/friction that hindered smooth fork motion.

Nitpicking Department: Using a 90° fitting isn't a deal killer, but if it isn't necessary use a straight fitting.

You have tested the paint for adhesion after being in contact w/gasoline, right? ;) Regardless, I'll bet carb spray will kill it- so be careful. Very unique, no doubt.
 
#71 · (Edited)
cobalt327 said:
The part you were wondering about the name is a "dashpot". It acts as a slight delay, preventing the throttle from 'slamming' shut. It's unnecessary for the most part.
EDIT- I see yours has a vacuum barb on it. This may still be just a dashpot, or an idle speed modulator of some type- I do not recall ever seeing a vacuum barb on a dash pot- so I'm at a bit of a loss as to what it is, exactly.

What action occurs when vacuum is applied to it- does it retract, or ?
Good question. I remember the guys who were helping me out on the thread about the truck told me to do a vacuum test but I could never keep it running long enough to do it.




cobalt327 said:
EDIT II- You will sometimes hear the choke pull off/unloader or secondary vacuum break called a "dashpot". The dashpot I'm referring to above (that checks the throttle closing) has nada to do w/the choke OR secondary action- just so we're clear on this. Because if you google "q-jet dashpot" (like I just did looking for info on why there'd be a vacuum barb on a dashpot), most of what comes up has to do w/the choke unloader/pull off.
Got it.




cobalt327 said:
[BTW, I saw nothing on a vacuum assisted dash pot, so I'm still at a loss. If I see something on this, I'll post it and you do the same. There were just SO MANY iterations of the Q-jet through the years that keeping up w/all of them is quite impossible- there always seems to be something different.
I hear you on that. I've read so much stuff the last couple of months I'm sure I've forgotten half of it.




cobalt327 said:
[Stiction" comes from the motorcycle magazines of the '70's. It was used by to describe the fork seal to fork tube stickiness/friction that hindered smooth fork motion.
I have to admit I had to Google it lol!




cobalt327 said:
[Nitpicking Department: Using a 90� fitting isn't a deal killer, but if it isn't necessary use a straight fitting.
I assume this is for the fuel inlet? I'll get a hold of a straight one as time permits.




cobalt327 said:
[You have tested the paint for adhesion after being in contact w/gasoline, right? ;) Regardless, I'll bet carb spray will kill it- so be careful. Very unique, no doubt.
... um, no... :sweat: ... lol! But its powdercoat on the airhorn, float bowl and throttle plate so I figure it should be quite strong. I did look up a few places that powdercoat carburetors and havent heard any issues. I did spray paint the small parts in metallic gold so they may likely be affected more easily. I'll do the carb spray "test' to see if anything comes off. Thanks for the props :D
 
#72 ·
On the 'dashpot', you can apply vacuum by mouth or a vacuum pump just to see what- if anything- happens on the plunger end (if there is a plunger- I'm assuming there is one that will bear on the throttle linkage).

There's a chance that it could be bad. If there's no action and/or it will not hold a vacuum, you can bet it has a leaky diaphragm.

In any event, I can think of no good reason to even keep it, unless something to the contrary comes to light.

Have you checked the choke unloader/secondary vacuum break to see if it's good?
 
#73 · (Edited)
cobalt327 said:
Figure 72, #67 HERE has a similar unit called an "idle load compensator", shown w/a throttle return spring arm attached to the bracket holding it.
cobalt327 said:
On the 'dashpot', you can apply vacuum by mouth or a vacuum pump just to see what- if anything- happens on the plunger end (if there is a plunger- I'm assuming there is one that will bear on the throttle linkage).

There's a chance that it could be bad. If there's no action and/or it will not hold a vacuum, you can bet it has a leaky diaphragm.

In any event, I can think of no good reason to even keep it, unless something to the contrary comes to light.
Honestly, I think it is part #69, the Actuator-Throttle Lever. Sorry, I can;t get to my stash of pictures while at work but when I compared them at home, they seem to match up. A hose runs from this "dashpot" to a device with a plastic cover on it on top of the manifold. This page from Carburetor-Manual.com gives the infio below:
THROTTLE LEVER ACTUATOR



Some heavy duty truck Quadrajet applications use a throttle return control (TRC) system. The system consists of a throttle return control valve, mounted separately from the carburetor, and a throttle lever actuator mounted on the carburetor float bowl on the throttle lever side (Figure 40).



The throttle return control valve is an on-off valve that senses engine manifold vacuum and opens above a preset high vacuum level. The valve, when open, allows a vacuum signal to be applied to the throttle lever actuator.
** From Carburetor-Manual.com

What do you think?




cobalt327 said:
Have you checked the choke unloader/secondary vacuum break to see if it's good?
No, I have not done that yet but will try to get to it today.
 
#74 ·
lt1silverhawk said:
Honestly, I think it is part #69, the Actuator-Throttle Lever.
I saw that, too. It screws to the driver side of the carb, not the front- but that could be just a different way of mounting the same device. If you had the other components of the system on the engine (this was a truck carb?) then I would readily agree.
 
#75 · (Edited)
cobalt327 said:
I saw that, too. It screws to the driver side of the carb, not the front- but that could be just a different way of mounting the same device. If you had the other components of the system on the engine (this was a truck carb?) then I would readily agree.
Yes, the carb is from a '77 Chevy truck (k20, heavy duty) with a crate 350. I'll try to get the pictures from the setup on here this afternoon.
 
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