Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level) - Page 3 - Hot Rod Forum : Hotrodders Bulletin Board
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  #31 (permalink)  
Old 02-07-2011, 03:39 PM
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Quote:
Originally Posted by cobalt327
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.
Oh yes, I have been searching and reading like crazy on this forum as well as others. Lots of info on turning it, which makes me a little less nervous since I don't know what to listen or look for right away. This will be a trial-and-error kind of lesson.




Quote:
Originally Posted by cobalt327
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.
Im glad you mentioned this. I was planning on reusing the old pin because I thought it might be a bit of a hassle to replace it and the original seems to fit snugly. I do need to invest in a feeler gauage and this tip will help in installing the pin correctly.




Quote:
Originally Posted by cobalt327
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.
The screws in this carburetor are the flat blade type, but Im glad you mentioned this because this information will definitely help someone else out. And I will also know what to look out for if I ever rebuild another one.




Quote:
Originally Posted by cobalt327
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).
These clips are available on quadrajetparts.com and carburetion.com. Since I will most likely be buying the power piston bushing, I'll add the clips to my order.




Quote:
Originally Posted by cobalt327
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.
Sorry, I am confused on this one. Do you mean the two bolts that attach the carburetor to the intake manifold or the the two bolts that attach the base plate (throttle body) to the float bowl?




Quote:
Originally Posted by cobalt327
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 haven't looked at these yet but will check tonight. I've also read that there can be some play in this area but not sure how to "tighten" it up. Any suggestions?




Quote:
Originally Posted by cobalt327
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.
OK, this will be something I will need to look up because Im not sure what part this is. But again, good to know in advance.




Quote:
Originally Posted by cobalt327
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.
I was originally considering using JB Weld. The author of the video series I've been watching on Youtube that details the Qjet tear down and rebuild recommended the use of 5 minuet epoxy and and that's what I need up using yesterday. I did discuss it with the manager of the local Autozone and he did caution that, while the heat resistance is fine (over 200 degrees F), nowhere on the packaging did it say that the epoxy is resistant to gasoline. I imagine I would have to take the carburetor to a professional for the permanent fix you mentioned.




Quote:
Originally Posted by cobalt327
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.
This will be another part I will need to look up further. Im hoping it won't get to this but at least I will know what to expect.




Quote:
Originally Posted by cobalt327
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.

Thanks for pointing that out, 'cause I was gonna toss 'em! Any idea what the little cork gasket is for?



Colbat, I cannot thank you enough for putting in all this time and effort in making this information available, and in such a straight forward and easy to understand format. This is going to help me and anyone else who refers to this thread tremendously.

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  #32 (permalink)  
Old 02-07-2011, 04:29 PM
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Quote:
Originally Posted by lt1silverhawk
These clips are available on quadrajetparts.com and carburetion.com. Since I will most likely be buying the power piston bushing, I'll add the clips to my order.
Just the clips won't help unless you also have the links w/the small hole or groove in/on it, depending on the style of clip that's used. The clips are often included in the rebuild kits since the kits cover many different carbs.

Quote:
Sorry, I am confused on this one. Do you mean the two bolts that attach the carburetor to the intake manifold or the the two bolts that attach the base plate (throttle body) to the float bowl?
The front long bolts that go all the way through the carb to the intake.

Something else comes to mind in this area- and that's to tighten the carb to the thick insulator-type gasket evenly but not too tightly. Because the gasket of that type has a lot of give to it, it can cause the base plate to warp- sometimes enough to cause the throttle shafts/blades to bind.

Quote:
I haven't looked at these yet but will check tonight. I've also read that there can be some play in this area but not sure how to "tighten" it up. Any suggestions?
Usually the play will be on the primary shaft. The shaft is teflon coated (that green colored material) but despite this, the shaft wears directly on the aluminum of the throttle plate. There are bushing kits to fix this if it's worn too much.

How much is too much? If you get an erratic idle or if it's obviously worn out. There will be play in ALL of them, though and that's where determining how much is too much is tricky. But if it idles good, it's good to go, IMO.

Quote:
OK, this will be something I will need to look up because Im not sure what part this is. But again, good to know in advance.
If you take the idle mixture screw out, it's the hole at the end of the threads.

Quote:
I was originally considering using JB Weld. The author of the video series I've been watching on Youtube that details the Qjet tear down and rebuild recommended the use of 5 minuet epoxy and and that's what I need up using yesterday. I did discuss it with the manager of the local Autozone and he did caution that, while the heat resistance is fine (over 200 degrees F), nowhere on the packaging did it say that the epoxy is resistant to gasoline. I imagine I would have to take the carburetor to a professional for the permanent fix you mentioned.
JB Weld will work, just not permanently, is all. I believe Ruggles has the plugs and possibly the primary screws should they be needed. But it's almost always the older (702/704xxxx carb numbers that have the problem. Newer carbs used a better plug arrangement and usually don't leak.

Another thing that is a stop-gap measure at best for a leaky well, is those black, 1/4"-3/16" thick foam rubber pieces that most carb kits include. They will work for a while, but are not permanent.

Quote:
This will be another part I will need to look up further. Im hoping it won't get to this but at least I will know what to expect.
Don't even worry about this, unless "you are experiencing a lag or slight bog (when the secondaries open up) that doesn't respond to the usual fixes- like the air valve spring tension adjustment or the unloader orifice size."

Quote:
Any idea what the little cork gasket is for?
It goes between the choke and carb body on hot air-type chokes.

Like you said, hopefully this will help someone doing a search, and because of your descriptive title, I was more inclined to add to your thread, so good job w/that. All too often, threads will get a title like, "Need Help". Or "Problem With My Engine". You know that any info in the thread will die w/the thread.
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  #33 (permalink)  
Old 02-07-2011, 11:32 PM
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Quote:
Originally Posted by cobalt327
Just the clips won't help unless you also have the links w/the small hole or groove in/on it, depending on the style of clip that's used. The clips are often included in the rebuild kits since the kits cover many different carbs.
I must admit that I am rather disappointed with this rebuild kit. I picked up thinking it would be a complete kit, but now it seems rather incomplete when compared to what others say should be included. For instance, there is no accelerator pump.




Quote:
Originally Posted by cobalt327
The front long bolts that go all the way through the carb to the intake.

Something else comes to mind in this area- and that's to tighten the carb to the thick insulator-type gasket evenly but not too tightly. Because the gasket of that type has a lot of give to it, it can cause the base plate to warp- sometimes enough to cause the throttle shafts/blades to bind.
Got it. There were four bolts when I removed the carburetor; two long ones in the front and two short ones in the back. I will take special care not to over-tighten the bolts when reinstalling.




Quote:
Originally Posted by cobalt327
Usually the play will be on the primary shaft. The shaft is teflon coated (that green colored material) but despite this, the shaft wears directly on the aluminum of the throttle plate. There are bushing kits to fix this if it's worn too much.

How much is too much? If you get an erratic idle or if it's obviously worn out. There will be play in ALL of them, though and that's where determining how much is too much is tricky. But if it idles good, it's good to go, IMO.
I will check for play but I will say, before rebuild, the idle seemed fine, though a bit low.




Quote:
Originally Posted by cobalt327
If you take the idle mixture screw out, it's the hole at the end of the threads.
Got it.




Quote:
Originally Posted by cobalt327
JB Weld will work, just not permanently, is all. I believe Ruggles has the plugs and possibly the primary screws should they be needed. But it's almost always the older (702/704xxxx carb numbers that have the problem. Newer carbs used a better plug arrangement and usually don't leak.

Another thing that is a stop-gap measure at best for a leaky well, is those black, 1/4"-3/16" thick foam rubber pieces that most carb kits include. They will work for a while, but are not permanent.
This carburetor is a (1)7057525, making it a 1977. I am hoping that since a layer of silicone was used to seal the wells in a previous rebuild, it doesn't have any leaks and the silicone was just precautionary.




Quote:
Originally Posted by cobalt327
Don't even worry about this, unless "you are experiencing a lag or slight bog (when the secondaries open up) that doesn't respond to the usual fixes- like the air valve spring tension adjustment or the unloader orifice size."
Not sure if it is related, but before the truck became victim of water and debris in the gas tank, it did suffer from slight hesitation / slight bog.




Quote:
Originally Posted by cobalt327
It goes between the choke and carb body on hot air-type chokes.
Then I won't be needing it since this one has the divorced choke.




Quote:
Originally Posted by cobalt327
Like you said, hopefully this will help someone doing a search, and because of your descriptive title, I was more inclined to add to your thread, so good job w/that. All too often, threads will get a title like, "Need Help". Or "Problem With My Engine". You know that any info in the thread will die w/the thread.
LOL! I'm glad my geeky work skills and an obsession with organization are paying off! I completely agree with you about the titles; nothing throws off a person more than a generic title that doesn't say what the thread is about. I'm sure I have passed over many a good threads with bad titles.



So, for now, I'll be ordering a new accelerator pump as well as the power piston retainer. I am considering new jets but don't know how to tell what size they are. In any case, the originals seem to have cleaned up well. I will also be buying the bit mentioned in the earlier post to clean out the two orifices.

In the mean time, if you feel that something else requires attention, please do point it out!
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Old 02-08-2011, 06:30 AM
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I don't want to rain on your parade but I think you are being penny wise and pound foolish by not investing in Cliff's book. There are some very simple and cost effective modifications he recommends for even a stock rebuild which will enhance the performance and reliability of the carb and greatly increase the chance of a successful rebuild. The lean idle qualities and accelerator pump circuit of the emissions era quadrajets specifically need to be addressed.

BTW he recommends Devcon Marine-Tex epoxy as the only permanent well plug sealing material he has found.

He is a great source for parts and has a forum where you can get advice and feedback on your rebuild. His rebuild kits are a little pricey but would have addressed some of the parts issues you have described.

Just my 2 cents. Take it for what its worth.
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Old 02-08-2011, 06:56 AM
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The jet and rod sizes are stamped into them. The jets have the number on the top surface as you look down at them orientated as if they were installed.

The rods (primary and secondary) have the size stamped onto the rod, you'll need to look for it, possibly use magnification (I do, but my eyes are old).

Earlier carbs used a jet that was about 30 numbers larger than the rod number. Later carbs the spread was less. This depends on the air bleed type, etc. and isn't anything you need be overly concerned with at this point- I would reassemble the carb w/the stock primary jets and rods first before changing anything. Then after the engine has run long enough for you to get ahold of the traits and plug readings you see, changes can be made if needed.

I have heard the Ruggles and Roe books are good. Most guys seem to say they like the Ruggles book better- it spells out "recipes" for different engine scenarios that can be followed.

People like to be told: "do this and then do that", rather than having to figure things out for themselves. This is fine, but leaves me wondering if that method actually helps anyone to actually understand the "cause and effect" of why a change does this or that.

But I digress- the book has had good reviews (that I assume also equates to successful carb builds), and I suppose that's what matters most.
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  #36 (permalink)  
Old 02-08-2011, 09:38 AM
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Hey TommyK,

Quote:
Originally Posted by TommyK
I don't want to rain on your parade but I think you are being penny wise and pound foolish by not investing in Cliff's book. There are some very simple and cost effective modifications he recommends for even a stock rebuild which will enhance the performance and reliability of the carb and greatly increase the chance of a successful rebuild. The lean idle qualities and accelerator pump circuit of the emissions era quadrajets specifically need to be addressed.

BTW he recommends Devcon Marine-Tex epoxy as the only permanent well plug sealing material he has found.

He is a great source for parts and has a forum where you can get advice and feedback on your rebuild. His rebuild kits are a little pricey but would have addressed some of the parts issues you have described.

Just my 2 cents. Take it for what its worth.
First off, I'm glad you brought up all of this.

I have read nothing but good reviews on Cliff Ruggle's "How to Rebuild and Modify Rochester Quadrajet Carburetors". Its true, I did try to cheap out by not buying the book and resorted to look for online articles and help instead. I actually tried to borrow one but that never worked out. However, now it only seems wise to buy a copy and read it thoroughly. (I'm working on a part timer's budget).

I never knew that there was an online shop/forum run by Cliff (Cliff's High Performance Quadrajets). Reading the previous posts, I noticed that cobalt327 did mention Ruggles as a good place for plugs but I never got a chance to look into what it was. Frankly, I am rather amazed that his website never came up when I was researching online. I like the fact that they can custom build a customer's rebuild kit and the starting price is the same as what I paid for my kit plus a new float. I did see the Devcon Marine-Tex epoxy. $20 plus shipping seems bit much but if it gets the job done then, I'll fork it out.

I'm going to try and purchase everything I need from Cliff's site, but I must say I couldn't find the power piston retainer anywhere on the site so I will inquire about that.

Since I have been picking everyone's brains on this forum, and several members have taken the time and energy to contribute tons of useful information on this rebuild, I will continue documenting it here. It is actually a part of another project which the forum members have been helping me with. However, I will now also use Cliff's forum to obtain any other necessary information and feedback. I am going to be away for a week so I'll probably do some reading then. (As of this writing, it seems that the big man has been out due to surgery and is still recovering).

TommyK, your two cents are worth alot more than that. Thank you for sharing this information. It has already helped me out and it will help someone in the future.




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




Good morning cobalt327!

Quote:
Originally Posted by cobalt327
The jet and rod sizes are stamped into them. The jets have the number on the top surface as you look down at them orientated as if they were installed.

The rods (primary and secondary) have the size stamped onto the rod, you'll need to look for it, possibly use magnification (I do, but my eyes are old).

Earlier carbs used a jet that was about 30 numbers larger than the rod number. Later carbs the spread was less. This depends on the air bleed type, etc. and isn't anything you need be overly concerned with at this point- I would reassemble the carb w/the stock primary jets and rods first before changing anything. Then after the engine has run long enough for you to get ahold of the traits and plug readings you see, changes can be made if needed.

Quote:
Originally Posted by cobalt327
I have heard the Ruggles and Roe books are good. Most guys seem to say they like the Ruggles book better- it spells out "recipes" for different engine scenarios that can be followed.
I have seen the same; people do seem to prefer the Ruggles book over Roe's. I was able to read portions of Doug Roe's "Rochester Carburetors" online and it seemed detailed and straight-forward.




Quote:
Originally Posted by cobalt327
People like to be told: "do this and then do that", rather than having to figure things out for themselves. This is fine, but leaves me wondering if that method actually helps anyone to actually understand the "cause and effect" of why a change does this or that.
I must admit that, for my style of learning, when I am working on something that I have zero knowledge (much like in this case)I prefer to be told what to do the first time around, with a simple explanation of "why". But after that, if I tackle the same job again, I find myself asking more detailed questions because I have some confidence and know what I am looking at. Which is why I have reread everything you and other members have posted several times over.




Quote:
Originally Posted by cobalt327
But I digress- the book has had good reviews (that I assume also equates to successful carb builds), and I suppose that's what matters most.
At this point, i think it is safe to say that this book definitely has a strong following (the one unhappy reviewer on Amazon complained about the fact that the author didn't go into the competition modifications). Well, its now on the shopping list.



Final shopping list (until something else comes up ): Power piston retainer bushing, accelerator pump, the bit for cleaning the orifices, and a copy of Ruggle's book.




By the way, cobalt327 and the rest of the forum members, I do wanna say that, due to circumstances in life, you guys are the closest thing to a shop teacher I may ever have, with this forum as the classroom and textbook. I really look forward to reading everything you guys have to say and teach.
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Old 02-08-2011, 10:03 AM
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Post #22 has a link to the split retainer for the PP if Ruggles doesn't carry them. Gessler also has most- if not all- of the hard to find small parts you could ever need.

Have you seen "Lars'" info on the Q-jet? If not, google "lars q-jet".

If the well plugs aren't leaking- leave them alone! The carb you have usually does NOT have this problem.
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Old 02-08-2011, 11:58 AM
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Quote:
Originally Posted by cobalt327
Post #22 has a link to the split retainer for the PP if Ruggles doesn't carry them. Gessler also has most- if not all- of the hard to find small parts you could ever need.
Yes, I did find the retainer on the Quadrajetparts.com. I didn't realize it was owned by Gessler. I was pricing my order on their site yesterday and it wasn't too bad. Had I known about them before, I would've taken advantage of the free shipping and ordered everything from their site.




Quote:
Originally Posted by cobalt327
Have you seen "Lars'" info on the Q-jet? If not, google "lars q-jet".
I just looked it up and wow! I've got some serious reading ahead of me (definitely feels like I'm back in school ). Here is a version in MS Word format




Quote:
Originally Posted by cobalt327
If the well plugs aren't leaking- leave them alone! The carb you have usually does NOT have this problem.
Yeah, I plan on leaving them be. To me, it seems the previous rebuilder had put a coat of silicone over the wells simply as a precaution. Besides, the epoxy has hardened and I haven't a clue how to remove it (aside from the Chem Dip, I suppose).
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Old 02-09-2011, 03:31 AM
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Just wanted to give an update on a few things (aka, a late night rant about nothing )...


I went ahead and ordered Cliff Ruggle's "How to Rebuild and Modify Rochester Quadrajet Carburetors", which should arrive this week. Since I am going to be away for a week, I'll go ahead and read up on it, along with Lars Grimsrud's "How to Tune a Q-Jet".


I went to Quadrajetparts.com, Carburetion.com, and Cliff's High Performance to price out my order for an accelerator pump, a power piston retainer bushing and a primary metering rod retaining spring for the power piston (mine seems a bit funky when compared to the way the new ones look).


While shopping for these parts, I noticed that sometimes the year application for certain parts didn't match up to what my carburetor currently has. For example, when searching for the primary metering rod retaining spring, I noticed on Quadrajetparts.com, the website says the spring I currently have (it is the oval-shaped one) is used in 1974 an earlier models (mine is a '77). For 1975 and up, the website shows this one.


An inconsistency I noticed between the three sellers is the correct choke pull-off (I'm not buying one, but was merely curious to see how much a replacement is). By matching up what I have with the pictures on the website (which can always be incorrect), I determined that I have what Cliff's refers to as the Chevrolet Straight-Inlet. However, while Cliff's website says it is applicable for years 1971-74, both Quadrajetparts.com says it for 19737-78 and Carburetion.com says it is for 1972-78. Of course, this is nothing that can't be clarified by contacting the sellers but just wanted to mention this for anyone else who does a price comparison with the three sellers.


All this prompted me to look up C & J Engineering, the local performance shop which at some point worked on my carb (they placed a small sticker for their company on the front of the carb that has since come off due to the dip). If something doesn't make sense, I figure I can always try and ask them about it as well.


So for now, I have decided to hold off on buying any replacement parts until I've read through the book and at least cleared up on the primary metering rod retaining spring.


I should be getting back to completing this in about a week and a half.


As always, thanks for the continued help!
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Old 02-09-2011, 06:41 AM
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I most often see the 'squared' primary rod retainer clip (below) used on the APT equipped carbs ('75-up). It is what is on the '86 non-feedback 4.3L Q-jet I have- that also has the larger 800 CFM casting, oddly enough.



I went back and looked at your PP. Your carb doesn't have APT by the looks of things, the PP would have a pin coming out of it near the top. So despite what the numbers say (you're sure of them?), it seems this is an earlier-type carb.

If you were ever interested in finding or needing a 800 CFM Q-jet, the easiest way by far is to source one from a late model truck, including the 5.7 and 5.0 V8's and the 4.3L V6 up to '86 they can be found as non-feedback w/"good" HEI distributors, too (w/o feedback; w/vacuum and mechanical advance).

About the PP retainer- I seem to remember some older carbs ('74-'75 and older?) using the metal clip retainer for the PP rather than the plastic clip. The years I cite may be off, but I'd want to look into your PP to be sure it ever used the plastic bushing/retainer in the first place- especially now that it appears the carb is an earlier design.

In any event, the numbers can be different than the published info. The 1705xxxx does usually mean '76-'79, though.
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Old 02-09-2011, 02:01 PM
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Hey cobalt!

Quote:
Originally Posted by cobalt327
I most often see the 'squared' primary rod retainer clip (below) used on the APT equipped carbs ('75-up). It is what is on the '86 non-feedback 4.3L Q-jet I have- that also has the larger 800 CFM casting, oddly enough.



I went back and looked at your PP. Your carb doesn't have APT by the looks of things, the PP would have a pin coming out of it near the top. So despite what the numbers say (you're sure of them?), it seems this is an earlier-type carb.
...
In any event, the numbers can be different than the published info. The 1705xxxx does usually mean '76-'79, though.
Yes, the numbers on carburetor are correct. I meant to post a picture of it at one point but thought it might be overkill at the time.

I decoded the numbers using Holistic Page's carburetor page. And according to Recarbo's website, apparently "it is a documented fact that Rochester didn't follow these rules 100%". When I disassembled the carburetor, I did not see a APT screw in there. Maybe I missed it?




Quote:
Originally Posted by cobalt327
If you were ever interested in finding or needing a 800 CFM Q-jet, the easiest way by far is to source one from a late model truck, including the 5.7 and 5.0 V8's and the 4.3L V6 up to '86 they can be found as non-feedback w/"good" HEI distributors, too (w/o feedback; w/vacuum and mechanical advance).
I'm not sure what cfm mine is but I've read that majority of the 4 bbl were 750 cfm. Is there a big difference between the 750 and 800 cfm versions? (I will admit that at this point, I have no clue what the significance of "w/o feedback; w/vacuum and mechanical advance" is.)




Quote:
Originally Posted by cobalt327
About the PP retainer- I seem to remember some older carbs ('74-'75 and older?) using the metal clip retainer for the PP rather than the plastic clip. The years I cite may be off, but I'd want to look into your PP to be sure it ever used the plastic bushing/retainer in the first place- especially now that it appears the carb is an earlier design.
When I took the carburetor apart, I do not recall ever removing any type of retainer bushing or clip from the PP. And I was photographing every step of the way. To me, it seems like the PP was held in position using the gasket between the float bowl and the air horn, with the air horn's weight providing the necessary pressure. Below are some recent pictures of the PP and float bowl, after cleaning and powdercoating. I can post larger ones if needed. I will also post a picture of the retainer spring in its present condition.
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Old 02-09-2011, 02:41 PM
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Quote:
apparently "it is a documented fact that Rochester didn't follow these rules 100%". When I disassembled the carburetor, I did not see a APT screw in there. Maybe I missed it?
You didn't miss it, the carb doesn't have APT like you'd expect it to have. Which brings us back to the italicized statement above about the less-than-100% certainty of the numbers being always correct. This is an obvious case where the numbers do not jibe w/what the carb actually is.

You should use something to carefully measure the length of the primary rods from tip to tip. The later carbs ('68-up) used a rod that is 2.4" long. The earlier carbs use a rod that's slightly longer.

There were cases of the longer 703xxxx-style primary rods being used in marine-type 170xxxxx stamped carbs. But these carbs also often used the earlier pivot float- which your carb doesn't have (which is a good thing, the earlier pivot/large float carbs were touchier re fuel pressure).

Quote:
I'm not sure what cfm mine is but I've read that majority of the 4 bbl were 750 cfm. Is there a big difference between the 750 and 800 cfm versions?
From an earlier THREAD I posted to:
Quote:
Originally Posted by cobalt327
1976-86 pickups, vans and medium duty trucks are a great source for 170-prefix 800 CFM carbs. All engines could have (and most DID have) the 800 CFM, even the 4.3L V6.

FWIW, the original carb on my '86 Sierra 4.3L V6 is a 800 CFM, w/forward-pointing fuel inlet.

As seen looking down into an assembled carb:
750 CFM-

800 CFM-


Below- as seen disassembled, the top image is of a 800 CFM venturi, 750 FCM below it. Arrow (above) and circle (below) indicate the 'bulge' seen only on the 800 CFM versions:

Until the later trucks, the 750 was much more common, the 800 was considered to be a "find".

But there is no real advantage to the 800 casting, IMO- unless you have an engine that actually NEEDS the extra flow.

The downside to the 800 CFM casting is the primary venturi is larger. This give slightly less response, although it is still better than most every other carb design due to the multiple booster arrangement.

The difference in airflow between the 750 and 800 carb:

Primary Flow for the Q-jet

175 to 185 CFM for 750CFM Q-jets

210 CFM to 225 CFM for 800 CFM Q-jets.

The 225 CFM figure is only for the one-year-only '71 Pontiac 455 HO 4M Q-jet. It lacked the outer booster rings found in the other carbs.

Quote:
I will admit that at this point, I have no clue what the significance of "w/o feedback; w/vacuum and mechanical advance" is.
Cars from '81-up and trucks (some as late as '87-up) used a feedback-type carb and distributor to work w/the "CCC" (Computer Command Control) emissions system of the day. The carbs are not good for modifying for use w/o a computer, the distributors lack a vacuum advance and some both vacuum AND mechanical advance, so are not good for use w/o a computer, either.

So basically, "feedback" equals computer controlled.

Quote:
When I took the carburetor apart, I do not recall ever removing any type of retainer bushing or clip from the PP. And I was photographing every step of the way. To me, it seems like the PP was held in position using the gasket between the float bowl and the air horn, with the air horn's weight providing the necessary pressure.
I don't recall there being a PP that didn't have either a plastic or a steel clip retainer. But before I would bank on it, I would ask Ruggles or another carb expert what their take on it was. It wouldn't surprise me to hear there was a short run of carbs that used nada to retain the PP- but I do tend to doubt it.

Last edited by cobalt327; 02-09-2011 at 02:46 PM.
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Old 02-09-2011, 05:00 PM
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You have a picture in post 24 that looks like it shows the PP with the retainer on it. It is not uncommon for the retainer to fail to positively secure the PP in its hole in and of itself. The solution is to take a chisel and gently stake the edge of the hole in one or two spots against the retainer.

Its in the book!LOL!
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Old 02-09-2011, 06:58 PM
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Quote:
Originally Posted by cobalt327
You should use something to carefully measure the length of the primary rods from tip to tip. The later carbs ('68-up) used a rod that is 2.4" long. The earlier carbs use a rod that's slightly longer.

There were cases of the longer 703xxxx-style primary rods being used in marine-type 170xxxxx stamped carbs. But these carbs also often used the earlier pivot float- which your carb doesn't have (which is a good thing, the earlier pivot/large float carbs were touchier re fuel pressure).
Well it was gonna happen sooner or later: time to buy a caliper!




Quote:
Originally Posted by cobalt327
From an earlier THREAD I posted to:
I don't think you meant to do it but the link comes back to this thread.




Quote:
Originally Posted by cobalt327
Until the later trucks, the 750 was much more common, the 800 was considered to be a "find".

But there is no real advantage to the 800 casting, IMO- unless you have an engine that actually NEEDS the extra flow.

The downside to the 800 CFM casting is the primary venturi is larger. This give slightly less response, although it is still better than most every other carb design due to the multiple booster arrangement.

The difference in airflow between the 750 and 800 carb:

Primary Flow for the Q-jet

175 to 185 CFM for 750CFM Q-jets

210 CFM to 225 CFM for 800 CFM Q-jets.

The 225 CFM figure is only for the one-year-only '71 Pontiac 455 HO 4M Q-jet. It lacked the outer booster rings found in the other carbs.
Excellent info! From what I can tell by comparing the pictures to my carb's pictures, its definitely a 750 cfm.



Quote:
Originally Posted by cobalt327
Cars from '81-up and trucks (some as late as '87-up) used a feedback-type carb and distributor to work w/the "CCC" (Computer Command Control) emissions system of the day. The carbs are not good for modifying for use w/o a computer, the distributors lack a vacuum advance and some both vacuum AND mechanical advance, so are not good for use w/o a computer, either.

So basically, "feedback" equals computer controlled.
Thanks for clearing up yet another mystery




Quote:
Originally Posted by cobalt327
I don't recall there being a PP that didn't have either a plastic or a steel clip retainer. But before I would bank on it, I would ask Ruggles or another carb expert what their take on it was. It wouldn't surprise me to hear there was a short run of carbs that used nada to retain the PP- but I do tend to doubt it.
I'm gonna talk to the members on Cliff's forum and see what I can find out.




Cobalt327, you are on a roll!




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




Hey TommyK,

Quote:
Originally Posted by TommyK
You have a picture in post 24 that looks like it shows the PP with the retainer on it. It is not uncommon for the retainer to fail to positively secure the PP in its hole in and of itself.
Yes, there is a cap at the top that does move up and down but doesn't fit snugly in the tube for the PP. But it doesn't seem damaged in any way either, at least to my untrained eyes.




Quote:
Originally Posted by TommyK
The solution is to take a chisel and gently stake the edge of the hole in one or two spots against the retainer.

Its in the book!LOL!
I'll believe it when I see it lol! The book should be here today or tomorrow.

Last edited by lt1silverhawk; 02-09-2011 at 07:07 PM.
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Old 02-09-2011, 07:43 PM
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Tommy has good eyes!

The retainer collar IS on the PP (below). It has become loose over time, and if too loose, staking it into position might not be a good idea (but it IS an option for a slightly loose retainer), unless a replacement couldn't be found. But Gessler has the split collar type for a couple bucks, so...

At least there's no more wondering on my part whether it used the steel retainer or what. Mystery solved.



AFA "on a roll", w/the good title, hopefully this thread will get used, and early on dinger (a mod) asked about putting it in the knowledge base- so all the more reason to put a little effort into it.
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