Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level) - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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  #16 (permalink)  
Old 01-28-2011, 06:18 PM
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**NOTE: This post specifically deals with the disassembly step only. I have already dipped and cleaned the carburetor and applied a coat of powder coating. I will post the pictures for those steps at a later time. This way, the members have a chance to comment on the disassembly portion first. Please do point out anything that doesn't look right or I should focus on before reassembly. Thanks!

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

- Disassembly -

During this stage, I kept the camera close and handy. There are lots of little parts and linkages to track. Not much to mention here except I did my best to keep track of everything that was disassembled.

In retrospect, someone with a memory as bad as mine might do well to take notes as well. Also, try to do all this in a close time frame if possible (no long breaks in between). That way, one is more likely to have a good memory of how everything gets put back together. Lesson learned.

Below are the pictures of everything as it was taken apart. If anything is incorrectly labeled, please do point it out.

Several members suggested that cookie pans be used to separate parts. I ended up using an egg cartoon that was sitting around to organize the parts (not dip and clean).

For you audio/visual people, I used the following Youtube videos as guides: Rebuild Part 2, Part 3, and Part 4



























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  #17 (permalink)  
Old 01-29-2011, 01:20 PM
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- Cleaning -


**NOTE: Use gloves, goggles and a full-sleeved shirt in a ventilated place when dealing with any chemicals. The dip will make it hard to breathe at times. Parts can also slip and fall back into the dip, which can splash onto your hands. Lesson learned.


The following steps were used in the cleaning process:

1. Dip all parts in Chem-Dip and allow to soak. I used a small baking tray within a larger one to avoid any spills or mess. I placed the smaller parts directly into the Chem-Dip can using the included plastic strainer

2. Clean parts using a cleaning brush.

3. Clean off the dip using a can of carb cleaner .

4. Wash off all parts with water.

5. Scrub and dry parts using rags/Shop Towels.

6. Scrape off the gunk at the bottom of the float bowl. I used a large flat screw driver, with the tip covered using a shop towel to avoid any scratches.

7. Bake parts in a dedicated oven (not used for baking) for 20 minutes at 350 degrees. This supposedly allows debris hidden in pores to come out. It also allows to properly clean a metal surface before powder coating.

8. Clean parts using acetone and rags/Shop Towels.













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Old 01-29-2011, 05:06 PM
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- Powder Coat and Paint -

Since I have the equipment available, I thought I would go ahead and spray a coat of powder coating before reassembly. In keeping with all the firsts for me in this project, this is the first time I've powder coated anything for myself.

I went ahead and reassembled the air horn, float bowl and throttle body without any bolts. My thinking was that this would make the masking easier and I could run a single ground wire to the throttle body. I then plugged all holes and masked off the top of the air horn.

I cheaped out and used regular masking tape. After the parts were cured in the oven, the tape left sticky gunk behind. It was easy enough to remove using the Chep-Dip and cleaning brush. However, painter's masking tape may be better. Lesson learned.

I really wanted to powder coat the smaller parts and linkages as well but due to time constraints, I chose to use high temperature metallic spray paint instead.

In retrospect, I would have really liked to paint the body a glossy black, and the logos and serials numbers red. Unfortunately, with the linkages in the way, it was too difficult, but still something worth trying the next time.

To be honest, the powder coating looks much better in the pictures for some reason. Had I done it all properly, I would've sprayed a second coat for the areas that were missed (minial). Overall, it looks good and does the job.




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Old 01-29-2011, 05:10 PM
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- Parts Match Up -

I went ahead and matched up as many parts as I could from the repair kit to the old parts. Some of them I haven't a clue if they would be needed or not, such as the small circular washer/gaskets. Hopefully one of you can chime in about that.

Below are the pictures from the match up. The new parts are on the left, and the old on the right.




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Old 01-31-2011, 11:03 AM
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I will begin the reassembly tonight. Any last minute tips, pointers or issues you see in the pictures that I should take care of?
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  #21 (permalink)  
Old 02-07-2011, 12:31 AM
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- Reassembly: Phase 1 -


Sealing the Well Plugs

According to research, it seems that the well plugs at the bottom of the float bowls in Q-jets are prone to leak. The plugs on this carburetor were sealed with some sort of silicone (you can see it in the disassembly pictures), but it came off in the dip. I went ahead and sealed it again using 5 minute epoxy (it was recommended in the Youtube video series I am using).






Attaching the Throttle-body to the Float Bowl

Once the epoxy sealed up, I bolted up the throttle body to the float bowl using the two bolts, with a gasket in between.






Installing New Check Ball






Reinstalling Jets






Preparing and Installing New Float Needle and Seat






Preparing and Installing New Float

The new float was prepared by hanging the new needle and installing the pivot rod. The float was then installed by placing the needle in the seat and installing the pivot rod in its brackets.

The height was adjusted according to the instructions. For this particular model, it is 11/32" of an inch. Once the float is installed, the height is measured from the toe of the float to the top of the float bowl wall. The height is adjusted by gently forcing the metal bar on the float up or down using some needle nose pliers.





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




Power Piston Retain Cap Question

After setting up the float, I tried to install the power piston but, the retainer cap at the top of the piston that pushes into the tube will not stay in place. I can only assume that I somehow damaged it during disassembly. Of course, now the piston doesn't stay in place and the rods aren't sitting in the jets.

Is there any fix to this, aside from purchasing a new piston or a replacement bushing? New parts are sold here.






As always, all help greatly appreciated!

Last edited by lt1silverhawk; 02-07-2011 at 12:46 AM.
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Old 02-07-2011, 01:11 AM
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Usually you would expect to see a plastic retainer (shown below). The plastic retainer is a tight enough fit to seal the PP, and retain it in the casting.



The retainer shown is a replacement of the original. It is 'split' to allow it to be installed w/o taking the PP apart.
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Old 02-07-2011, 06:39 AM
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An OFTEN overlooked passage that needs to be cleaned, and is often plugged or obstructed, is the small, ~0.028" orifice that connects the secondary discharge port well to the main fuel reservoir.

Because it's on a 'ledge', it's prone to have deposits clog it, and it is hard to see if you're not specifically looking for it.

Be careful to not enlarge this orifice, it is also part of the secondary air/fuel ratio calibration and if made too large, will cause the secondary to go pig rich under extended WOT operation.

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Old 02-07-2011, 10:37 AM
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Hey Cobalt,

Quote:
Originally Posted by cobalt327
Usually you would expect to see a plastic retainer (shown below). The plastic retainer is a tight enough fit to seal the PP, and retain it in the casting.


I was looking over the pictures from disassembly and it seems the power piston was held down in place using the gasket that lays between the float bowl and the air horn. I tried doing that and it works, as long as the gasket is held down in place and the air horn is quickly placed on top. Otherwise, due to the spring below it, the piston is prone to jump out a bit. I personally don't see this as ideal solution. Any thoughts?







Quote:
Originally Posted by cobalt327
The retainer shown is a replacement of the original. It is 'split' to allow it to be installed w/o taking the PP apart.
I was looking at what's left in the rebuild kit and found three round gaskets, one rod for the fuel pump, and the accelerator pump cap. The small brown cork gasket fits perfectly in the area where the power piston is placed. However, it wasn't pre-cut in any way so I assume its not for that. Worse comes to worse, I order the bushing.





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




Quote:
Originally Posted by cobalt327
An OFTEN overlooked passage that needs to be cleaned, and is often plugged or obstructed, is the small, ~0.028" orifice that connects the secondary discharge port well to the main fuel reservoir.

Because it's on a 'ledge', it's prone to have deposits clog it, and it is hard to see if you're not specifically looking for it.

Be careful to not enlarge this orifice, it is also part of the secondary air/fuel ratio calibration and if made too large, will cause the secondary to go pig rich under extended WOT operation.
I tried looking for these passages but was not able to find 'em. I'll admit Im not very good with the proper terms for different parts so that may be throwing me off. Below is a picture of what I was looking at. feel free to copy and mark as needed.






Thanks for the help and pointers!
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Old 02-07-2011, 11:35 AM
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While the photo I used isn't quite clear enough to make out the orifice, the black arrows point to the area where they should be found.



The outermost brass tubes that extend down from the top of the carb (aka the "airhorn") on the secondary side, enter the fuel-filled reservoirs (red arrows, filled by those orifices).

Fuel is picked up as the secondaries begin to open and enters the airstream through two small holes just beneath (usually- the holes can also be above) the secondary air valve. This acts as an auxiliary fuel circuit, as well as a passive accelerator 'pump' to enrichen the fuel/air mixture as the secondaries just begin to tip in.

Without this, a bog will occur when the secondaries are called on.
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Old 02-07-2011, 12:08 PM
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Quote:
Originally Posted by cobalt327
While the photo I used isn't quite clear enough to make out the orifice, the black arrows point to the area where they should be found.

So, I removed the float assembly, and voila, found 'em! The entire time, I was looking for orifices that ran vertically. Based on the "light" test, they seem open and unclogged. They are very very small. What would be the proper tool/method for cleaning them?





Thanks for the help!
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Old 02-07-2011, 12:18 PM
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the best advise i can give u is trash your quadrajunk. ive got one in a million peaces on my back porch that can tell the story of endless nightmares. they are the best carbs to have when thet work good but once the go bad its damn near impossible to get them right again. get yourself an edelbrock, u wont regreat it. if your quadrajet meens something to you then fix it, i got tons of parts lol
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Old 02-07-2011, 12:23 PM
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The best tool for this job is the blunt end of a #70 drill bit.

Click on image for the site the image is from. Hobby shops also carry these small bits. The common sets range from #61 (0.039") to #80 (0.0135").
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Old 02-07-2011, 01:57 PM
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Hey Josh,

Quote:
Originally Posted by Josh dalrymple
the best advise i can give u is trash your quadrajunk. ive got one in a million peaces on my back porch that can tell the story of endless nightmares. they are the best carbs to have when thet work good but once the go bad its damn near impossible to get them right again. get yourself an edelbrock, u wont regreat it. if your quadrajet meens something to you then fix it, i got tons of parts lol
Lol! My original thought was to ditch the Qjet as well and throw on a Holley I've got sitting around. But after several people mentioned that this setup will indeed be the best one - once its properly tuned - it just seemed like a good opportunity to learn something new and get over my fear of carburetors (and we all fear what we don't understand). While everything has been pretty much smooth sailing so far, due in large part to all the help from the members of this forum, I hit my first bump in the road with the power piston. But if anything makes me nervous now, it is definitely the tuning.

How many parts you got? I just may tackle another one lol!




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




Quote:
Originally Posted by cobalt327
The best tool for this job is the blunt end of a #70 drill bit.

Click on image for the site the image is from. Hobby shops also carry these small bits. The common sets range from #61 (0.039") to #80 (0.0135").
Sweet! I'm sure I can pick it up localy. Thank you for your continued help Cobalt!
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Old 02-07-2011, 03:06 PM
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You are quite welcome. FWIW, there are a LOT of threads on working w/the Q-jet here on the forum. If you haven't yet done so, a search might be of some use to you.

There are a few tips and tricks, like placing a ~0.050" feeler behind the accelerator pump lever pin, so when you drive the pin towards the air horn lip it doesn't butt tightly against it- instead there's room to get a thin straight blade screwdriver in behind it to lever the pin back into position.

There are several different heads to the idle mixture screws: hex, flat blade slot, and one is an ovoid/hex affair that defies all logic- other than to make it difficult to turn. You'd have thought that capping the screws would have been enough, but I suppose this was extra insurance that they wouldn't be tampered with.

Anyway, these ovoid screws can be removed by using a crimped length of brass tubing, found at hobby shops. Once these bastard screws are out, use a dremel and a cutting disc to put a slot in them for a standard screwdriver. I do this to ALL my carb's idle mixture screws, because finding the right sized 1/4" drive deep socket is only half the battle- the OD of the socket has to be ground down in many cases in order for the socket to fit into the available space.

Early Q-jets had accelerator pump and choke linkages that were secured by small clips. If you can get your hands on these, they make dis- and re-assembly easier (especially the acc. pump link).

For some reason, I have found the base plate on many Q-jets to be missing a screw or two. While the base plate is "helped" being held on by the two long front bolts, it's still a good idea IMO to go ahead and add the missing screws. Just be sure to not over tighten these long bolts. If they're over tightened, it can warp the carb beyond use.

Check the base plate to be sure the throttle blades are exactly 90 when wide open. There are some who believe having the secondary throttle blades go "over center" helps w/A/F distribution w/some intakes. While this may be true, until you have a good grasp on the engine's tune and plug readings indicate a need for this, keep them @ 90.

I don't want to get you sidetracked w/a lot of tuning 'advice', this being a primer for dis- and re-assembly. But this is an easy cure for a common problem you might run into:

The idle discharge ports that are controlled by the idle mixture screws can be anywhere from around 0.050" to 0.080". If you find a lean idle condition that doesn't seem to respond to turning out the screws CCW, you can gauge the port size then enlarge it one size at a time until you regain control w/the screws.

This is providing that the throttle plates are not open too far due to a large cam- which will over-expose the transfer slot, just like on a Holley. The cure for that is the same as you'd do w/a Holley- start by using more ignition advance. This allows the primary throttle blades to be closed down some to lower the idle speed, which increases due to the advanced timing. Often, this is all that's needed, so be sure to do this FIRST, then enlarge the ports only if still needed.

A common problem on the early Q-jets especially, is leaky main wells.

The 'cure' for this has long been to use JB Weld, etc. to seal them over. This is just a stop-gap measure, I have seen personally how the epoxy will degrade over time and quit sealing as it did at first.

If a permanent fix is wanted, the wells can be resealed w/new plugs that are peened over to hold them in place.

The primary wells can be drilled and tapped for short screws that will cure them for good, although these wells seldom leak.

One last thing before this gets any more long-winded. On the secondary accelerator 'pump' discharge ports that are often located above the air valve- these are better located just below the closed blades. The upper ports can be sealed off w/epoxy on a clean, roughed up surface then the same size ports located under the blades, in line w/the existing holes.

Only do this if you are experiencing a lag or slight bog that doesn't respond to the usual fixes- like the air valve spring tension adjustment or the unloader orifice size.

The center two round gaskets are for the two different types of fuel filter housing/inlet fittings that were used. One uses the white nylon gasket on the very end of the housing, the other type used the orange gasket all the way to the end of the threads. If there's a lip on the end of the housing that will accept the white nylon gasket- use it, not both.

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