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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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8
#77 ·
- Mystery Dashpot -


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.
I feel the "mystery dashpot" is indeed the Throttle Lever Actuator. The system as described here seems to match. The only issue is, the nut in the front is twisted in a "locked" position so that it doesn't move (see picture below). Perhaps the intention of the previous rebuilder or owner was to permanently set a maximum throttle? Please refer to the set of pictures in the previous post for more angles.






cobalt327 said:
What action occurs when vacuum is applied to it- does it retract, or ?
After unlocking the nut, I did test it by sucking on it and it moves perfectly with out requiring much pressure.



Please do chime in if you have anything to add or correct. Thanks :thumbup:
 
#78 ·
I've never seen, adjusted or otherwise dealt w/such a device, but then I've not hotrodded or even worked on 20-series truck emission devices.

GM came up w/a LOT of Rube Goldberg-ish devices to deal w/emissions, and this is yet another one that needs to be relegated to the trash bin- as long as your jurisdiction's emission testing doesn't require you to keep it.

I would consider it TOTALLY superfluous and I wouldn't hesitate for an instant to remove it and it's related encumbrances- or at the very least to render it inoperable (like what seems to have been done previously) and retain it for visual inspection compliance only.
 
#79 ·
cobalt327 said:
GM came up w/a LOT of Rube Goldberg-ish devices to deal w/emissions, and this is yet another one that needs to be relegated to the trash bin- as long as your jurisdiction's emission testing doesn't require you to keep it.

I would consider it TOTALLY superfluous and I wouldn't hesitate for an instant to remove it and it's related encumbrances- or at the very least to render it inoperable (like what seems to have been done previously) and retain it for visual inspection compliance only.
I have a strong feeling it is because of emissions that it was kept (it is California, after all). But then the only issue is, this truck is missing an EGR valve and the intake doesn't have the provisions to install one. Boy I would love to talk to the guy who worked on this. :confused:

By the way, just for added info, the device on the manifold that provides vacuum to the actuator is also connected to the carb via hose up front. below are pictures with the cap off, as well as the inlet/out let where the other hose slips on. (Sorry, should've done this a while back).

 
#80 ·
lt1silverhawk said:
I have a strong feeling it is because of emissions that it was kept (it is California, after all). But then the only issue is, this truck is missing an EGR valve and the intake doesn't have the provisions to install one.
Not having an EGR valve is common w/the larger truck series. So even though the aftermarket intake was bought w/o one, it probably didn't have one originally. Considering how everything else seems to have been retained that had to do w/emissions, it would have been easy to replace the intake w/an EGR-equipped version if the engine had an EGR to begin with.

You should be able to determine whether an EGR was necessary when the truck was made by checking w/the emission refs or possibly online. You will probably have to go by the gross vehicle weight.
 
#81 ·
cobalt327 said:
Not having an EGR valve is common w/the larger truck series. So even though the aftermarket intake was bought w/o one, it probably didn't have one originally. Considering how everything else seems to have been retained that had to do w/emissions, it would have been easy to replace the intake w/an EGR-equipped version if the engine had an EGR to begin with.

You should be able to determine whether an EGR was necessary when the truck was made by checking w/the emission refs or possibly online. You will probably have to go by the gross vehicle weight.
Well, the local smog police (aka smog shops) didn't even want to smog test my truck because the EGR valve was missing. The mechanic looked it up in his book and it said that it was supposed to have come with one (assuming it is a California truck, which I believe it is). The motor itself isn't the one the came originally came with either (provided the Goodwrench 350 valve covers werent just tossed on). But of course, you do have a point when you say that the rest of the emissions equipment was retained.

I'll see if I can dig up some info online.

Thanks! :thumbup:
 
#82 ·
- Idle Screws -

I went ahead and reinstalled the two idle mixture screws and the idle adjusting screw. I put them back in the same length they were before assembly by mtaching them up with the pictures. Not the most accurate way, but it is a start.






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




- Completed Carburetor -






This concludes the rebuild. Endless thanks to everyone who helped get this far. :)




Tomorrow, I should have the carburetor installed back on the truck and begin tuning it. Due to the fact the truck this carburetor is being used in was having fuel delivery and ignition problems, I am debating whether I should continue covering the tuning portion on that thread (1977 Chevrolet K10 - Starting Problems, Weak Idle and Power Loss). My reasoning is that, because the truck was having issues that eventually led to the carburetor needing the rebuild, it may not be appropriate for this thread, since the issues will be specific for my truck. However, if anyone feels otherwise, please do mention it.

Any tips and tricks on what to look out for and expect when tuning are greatly appreciated. :thumbup:
 
#86 ·
V8&4spd said:
That red carb must really set off the smog police. They notice anything that does not look stock. It might be a good idea to have a extra carb when you get it smogged. No smog here, anything goes.
Oh it is getting ridiculous with smog here. I remember "Hot Rod" did an article a few months back back about the California Air Regulatory Board (C.A.R.B.). The writers held a meeting with them about smogging their Crusher Camaro with a newer engine back in the 90's. Long story short, although the Camaro put out excellent emissions results with the newer motor (comparable to the modern cars of the time), the boys at CARB said that the smog shops would lose money if the visual inspection portion was eliminated.

As for me, the biggest concern is not having an EGR and, as cobalt327 pointed out, I need to look up whether it came with one or not.
 
#87 ·
- Reinstallation -


For reinstallation, I pretty much went in reverse of of what I did during the removal process. The pictures came in very handy. I did secure everything down, but did not fully tighten in case it had to removed. I also did not install the throttle lever actuator at this time, so as to have more space to access the idle adjusting screw.






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




- Initial Startup -

The battery seemed to be holding some juice after being parked for over two months so I thought I'd go ahead and fire it up. You can see the video of here. The truck didn't start and the battery began to die. I hooked the battery up to the charger and also noticed that I had not installed the choke as well as the small hose that runs from the choke pull-off to the carburetor. Please see images above for reference. The video shows that the linkages seem to be working and the fuel can be seen being delivered in the glass-cased filter.

After setting up the choke, linkage, the small rubber hose and also charging up the battery I gave it another go. You can see the video here. This time, the truck still struggled to start and would die right after catching on. I gave it gas a few times. Unfortunately, I did not realize that the rod connecting the choke to the linkage and come out of place. in the end, I saw a flame shoot out of the carb and immediately stopped everything.

As of now, the battery is charging, and some Stabil has been added to the gas tank. I still need to put the choke rod back in place. A Youtube video by HolleyPerformance gave some info as to what causes backfires and how to eliminate them.

Aside from the choke not working and possible ignition issues, anything else I should be on the lookout for?
 
#90 · (Edited)
V8&4spd said:
A quick way to check for bad gas is to buy a few feet of rubber fuel line and hook one end to the fuel pump and put the other end in a gas can of fresh gas. Also check your spark plugs to see if they are fouled.
Bad gas is what eventually led to the rebuild. Somebody dumped water and debris into one of the gas tanks. And its always possible that the gas I put in afterwards has also gone bad from sitting around for a couple of months. The spark plugs I do plan to check asap. I think there is a gapping issue.





V8&4spd said:
Do you have a thick base gasket? If not, use a thick base gasket and make sure the carb it tightened down good. Plug all the vacuum ports on the carb until after you get it running, that way you will know if there are any problems before you put them back on.
That's what I forgot! The base gasket! And yes, it does appear to be very think when compared to the other gaskets used. (Is it obvious that I am getting carried away by the excitement of finishing this, to the point that I'm forgetting things? Lesson learned).

Thanks for pointing that out V8. :thumbup:
 
#92 ·
V8&4spd said:
A vacuum leak can cause fits. If you put a brand new base gasket and hold the carb up to the light will be able to see day light between the base gasket and carb. Aftermarket intakes don't have as much sealing area as the factory intakes.
So basically, too much air being pushed out through the open spaces between the intake manifold (this one has an Edlebrock) and the carburetor's base gasket can cause issues?
 
#95 ·
- Reinstallation, cont'd. -


This morning, I went ahead and installed the base gasket, and reinstalled the the rod from the choke coil to the linkage. In retrospect, I believe it would be easier to setup the rod and linkage before placing the carburetor back on the manifold, and simply screwing down the choke afterwards.







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




- Startup: Take 2 -


Once everything was set, I sprayed some starting fluid into the carb and started her up again. You can see a video here. From what I can see, everything seems to be functioning fine. There is a bit of a "bop bop" sound in the exhaust that someone in the other thread mentioned might be a skip. At 2:18, I rev the engine to roughly 2500 rpm and hold it there for a few seconds.
 
#98 ·
V8&4spd said:
Forgetting the base gasket was the problem you were having with the backfire when you tried to start it up the first time. There can't be any vacuum leaks or there will be problems. I might have a book for the emissions that will cover your truck.
Yes, the missing presence of the gasket definitely turned the carb into a flame thrower lol! If you could possibly dig up some info on the truck, I'd greatly appreciate it. :thumbup:




123pugsy said:
Sounds real smooth.
Congrats on the rebuild.
Thank you 123pugsy! I appreciate the encouragement and props! Hopefully, other nervous rookies like me can tackle this too. :D

There is a bit of backfire in the exhaust when revved (the same issue the truck was having before the whole water in the gas tank deal). So next I need to recheck the wires and plugs. I still think the plugs were gapped in a way as to hide some issues by the previous owner. I went with the same gap when I changed them.
 
#100 · (Edited)
Ok, so the truck definitely "needs" to have an EGR. And it seem to be connected via a hose to the EGR TVS, which I believe is the manilfold-counted device that also runs the throttle lever actuator, aka "mystery dashpot", which is currently not hookeup.

By the way, the actuator is held in palce by a bolt. Even though I didn't install the actuator, this morning I went ahead and screwed the bolt back in its place out of fear of possible leaks.

Thanks V8!
 
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