Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level) - Page 5 - Hot Rod Forum : Hotrodders Bulletin Board
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  #61 (permalink)  
Old 03-21-2011, 11:27 PM
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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.


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  #62 (permalink)  
Old 03-22-2011, 12:04 AM
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Hey cobalt,
Quote:
Originally Posted by cobalt327
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.



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




Quote:
Originally Posted by cobalt327
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,
Quote:
Originally Posted by willys36@aol.com
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. 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!
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  #63 (permalink)  
Old 03-22-2011, 10:28 AM
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**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.


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  #64 (permalink)  
Old 03-24-2011, 09:45 AM
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Quote:
Originally Posted by cobalt327
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.

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  #65 (permalink)  
Old 03-24-2011, 10:45 PM
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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?

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  #66 (permalink)  
Old 03-25-2011, 12:40 AM
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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.
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  #67 (permalink)  
Old 03-25-2011, 06:42 AM
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Hey cobalt,

Quote:
Originally Posted by cobalt327
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.




Quote:
Originally Posted by cobalt327
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).




Quote:
Originally Posted by cobalt327
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
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  #68 (permalink)  
Old 03-25-2011, 08:10 AM
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- 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?

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  #69 (permalink)  
Old 03-25-2011, 08:37 AM
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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.

Last edited by cobalt327; 03-25-2011 at 09:06 AM.
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  #70 (permalink)  
Old 03-25-2011, 09:21 AM
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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.
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  #71 (permalink)  
Old 03-25-2011, 10:58 AM
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Quote:
Originally Posted by cobalt327
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.




Quote:
Originally Posted by cobalt327
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.




Quote:
Originally Posted by cobalt327
[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.




Quote:
Originally Posted by cobalt327
[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!




Quote:
Originally Posted by cobalt327
[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.




Quote:
Originally Posted by cobalt327
[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... ... 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

Last edited by lt1silverhawk; 03-25-2011 at 11:14 AM. Reason: More info added.
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  #72 (permalink)  
Old 03-25-2011, 11:14 AM
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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?
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  #73 (permalink)  
Old 03-25-2011, 11:14 AM
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Quote:
Originally Posted by cobalt327
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.
Quote:
Originally Posted by cobalt327
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:
Quote:
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?




Quote:
Originally Posted by cobalt327
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.

Last edited by lt1silverhawk; 03-25-2011 at 11:18 AM. Reason: More info added.
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Old 03-25-2011, 11:24 AM
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Quote:
Originally Posted by lt1silverhawk
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.
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Old 03-25-2011, 11:26 AM
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Quote:
Originally Posted by cobalt327
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.

Last edited by lt1silverhawk; 03-25-2011 at 11:41 AM. Reason: More info added.
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