Rebuilding rochester quadrajet

[mustangandy]

My 429 CJ (ram air, auto, non AC) has a holley in place of the rochester as the PO couldn't get it to run properly. I've now, thankfully, received the original carb. It's been boxed up for the last 3 years, stored dry, though there seems to be a fair bit of rust and gunk on it. If it was anything like it is now when it was pulled then perhaps that's why it didn't really work.

Does it look like all the original parts are with it?

I guess it's going to need a full strip, clean and rebuild. I've got the 'rebuild and modify Rochester quadrajet carburettors' book by Cliff Ruggles on the way, need to get a rebuild kit of course and then my plan was to just follow what it says. Does this sound sensible? I've not rebuilt a carb before but can take whatever time it will take, there's no rush. I've come across a few video's on you tube as well that look like they'll be helpful too.

If anyone has any other tips, tricks or suggestions they would be most gratefully taken.

Many thanks

 

[MikeGriese]

I would recommend a trip through an ultrasonic cleaner and soda blasting. It should clean up nicely.

 

[mustangandy]

I would recommend a trip through an ultrasonic cleaner and soda blasting.  It should clean up nicely.

Thanks Mike, however unfortunately I'm in the middle of nowhere in rural France so that might not be easily doable I'm afraid. I'll look around though, you never know!

 

[mustangandy]

I would recommend a trip through an ultrasonic cleaner and soda blasting.  It should clean up nicely.

Thanks Mike, however unfortunately I'm in the middle of nowhere in rural France so that might not be easily doable I'm afraid. I'll look around though, you never know!

 

[MikeGriese]

There are some dry ice strippers in the UK. Check on eBay under Lotus parts - I seem to recall seeing ads for services there. They have pretty low rates and quick turnaround. Take lots of pictures, strip the carb and send it off for a week. You can clean up the remaining parts while it is away.

 

[TommyK]

Do you have the divorced choke mechanism that sits in the well in the intake manifold?

Cliff's book is a good guide for the rebuild. Don't do any of the modifications or "recipes" for improving the operation. Just do a stock rebuild.

 

[Don C]

You can download the original GM service manual here

https://www.carburetor-parts.com/Free-Carburetor-Manuals_ep_274.html

 

[7173Vert]

What is the casting # and mfr. date code on the housing of the carb? I have included a couple pics of mine to show the location of these #'s for reference. Unfortunately on mine in this pic., you can only see "550" of the date code in the bottom number. The camera angle failed to pick up the additional "3" in front of the first "5"; so that it should (and does) read "3550". This number equates to an approximate December 22, 1970 carburetor build date, which is very close to my car's actual build date. 

The number on top in my pic: "7042086" is the correct carb mfr'd for my car which is a J Code C-6 auto and A/C. Your's should read with an "8" instead of the "6" on the end of this number (7042088). This will tell you if you actually have the correct as delivered carburetor for your engine/car. With this info., you can then determine what parts should be on the carb you are showing here.

 

[mustangandy]

OK after a bit of cleaning it seems that I don't, in fact, have what would be the original CJ Rochester carb. The number stamped into the body is 17059253 which means it is a 1979 M4MC quadrajet. It is made by Rochester, again stamped on body, and is 800cfm rather than 750cfm. It should have larger primaries as a result. I think that being a post 1975 carb means that it is the modified version, though I don't know what difference that would make. Again, from a bit of reading, it seems these are sometimes regarded as smog era carbs due to very lean fuel metering - would that be true? That's about everything I've found out so far.

I presume it was fitted as a replacement due to some problem with the original quadrajet carb.

Does the fact that I have this modified version of the quadrajet have an impact on trying to rebuild it and put it back on the car? Different rebuild kit I know. Would it have any advantages over the original, smaller quadrajet? Or the holley 3310 I now have on the car?

Thanks once more.

 

[mustangandy]

What is the casting # and mfr. date code on the housing of the carb? I have included a couple pics of mine to show the location of these #'s for reference. Unfortunately on mine in this pic., you can only see "550" of the date code in the bottom number. The camera angle failed to pick up the additional "3" in front of the first "5"; so that it should (and does) read "3550". This number equates to an approximate December 22, 1970 carburetor build date, which is very close to my car's actual build date. 

The number on top in my pic: "7042086" is the correct carb mfr'd for my car which is a J Code C-6 auto and A/C. Your's should read with an "8" instead of the "6" on the end of this number (7042088). This will tell you if you actually have the correct as delivered carburetor for your engine/car. With this info., you can then determine what parts should be on the carb you are showing here.

Thanks for the suggestion, I would have assumed it to be the original CJ carb, however sadly it's not, still a Rochester quadrajet but from 1979.

 

[7173Vert]

OK after a bit of cleaning it seems that I don't, in fact, have what would be the original CJ Rochester carb. The number stamped into the body is 17059253 which means it is a 1979 M4MC quadrajet. It is made by Rochester, again stamped on body, and is 800cfm rather than 750cfm. It should have larger primaries as a result. I think that being a post 1975 carb means that it is the modified version, though I don't know what difference that would make. Again, from a bit of reading, it seems these are sometimes regarded as smog era carbs due to very lean fuel metering - would that be true? That's about everything I've found out so far.

I presume it was fitted as a replacement due to some problem with the original quadrajet carb.

Does the fact that I have this modified version of the quadrajet have an impact on trying to rebuild it and put it back on the car? Different rebuild kit I know. Would it have any advantages over the original, smaller quadrajet? Or the holley 3310 I now have on the car?

Thanks once more.

The original is closer to the 715cfm, so your's is a little larger. I'm sure the engine can handle it with a good tune. Not sure of any advantages, the Rochester is a good carb if tuned properly, but some people have a lot of issues with them and put on another brand. I had to get this rebuilt unit properly tuned by a Master GM mechanic who knew the in's and out's of these carbs. Hopefully, I can keep it running in the same manner moving forward. FYI, I noticed in your original picture some differences in the carb, that is why I posted this info for you to consider as you move forward. To find (if you can, very scarce today...) a correct Ford modified GM Rochester carb. will run you $600-$1000 in original unrestored condition. Add another $500-1000 if it is complete and restored like mine. I paid $1500US for the one in the picture three year's ago, but the key for me with this purchase was the close carb mfr. date which coincided with the build date of my car. Mind you, I did a rotisserie restoration and wanted all original and date coded parts on the restoration, where possible. 

 

[mustangandy]

OK after a bit of cleaning it seems that I don't, in fact, have what would be the original CJ Rochester carb. The number stamped into the body is 17059253 which means it is a 1979 M4MC quadrajet. It is made by Rochester, again stamped on body, and is 800cfm rather than 750cfm. It should have larger primaries as a result. I think that being a post 1975 carb means that it is the modified version, though I don't know what difference that would make. Again, from a bit of reading, it seems these are sometimes regarded as smog era carbs due to very lean fuel metering - would that be true? That's about everything I've found out so far.

I presume it was fitted as a replacement due to some problem with the original quadrajet carb.

Does the fact that I have this modified version of the quadrajet have an impact on trying to rebuild it and put it back on the car? Different rebuild kit I know. Would it have any advantages over the original, smaller quadrajet? Or the holley 3310 I now have on the car?

Thanks once more.

The original is closer to the 715cfm, so your's is a little larger. I'm sure the engine can handle it with a good tune. Not sure of any advantages, the Rochester is a good carb if tuned properly, but some people have a lot of issues with them and put on another brand. I had to get this rebuilt unit properly tuned by a Master GM mechanic who knew the in's and out's of these carbs. Hopefully, I can keep it running in the same manner moving forward. FYI, I noticed in your original picture some differences in the carb, that is why I posted this info for you to consider as you move forward. To find (if you can, very scarce today...) a correct Ford modified GM Rochester carb. will run you $600-$1000 in original unrestored condition. Add another $500-1000 if it is complete and restored like mine. I paid $1500US for the one in the picture three year's ago, but the key for me with this purchase was the close carb mfr. date which coincided with the build date of my car. Mind you, I did a rotisserie restoration and wanted all original and date coded parts on the restoration, where possible. 

I wish that a rotisserie was in my plans but sadly that's never going to happen. I'll just keep her on the road, look after her and update parts etc as I need to. As I'm in Europe everything here tends to be at least 25% more expensive than in the US so, even if findable, I couldn't lay out near $2000 for a correct date carb, much as I'd like to! Same with things like batteries etc, correct style probably $400 and I could buy a comparable one here for $150. Needs must. I gather that a unique feature of the quadrajets is that, no matter their cfm rating, they will only pull what the engine requires so you can't go too big with them? I hope I can rebuild the quadrajet (I've plenty of time as retired and a rebuild kit is only $100). I've read plenty that they are tricky to tune properly but I'll take my time and, hopefully, with book, youtube and other sources of info, like this excellent site and knowledgeable and enthusiastic owners, I'll get there!

 

[mustangandy]

Do you have the divorced choke mechanism that sits in the well in the intake manifold?

Cliff's book is a good guide for the rebuild. Don't do any of the modifications or "recipes" for improving the operation. Just do a stock rebuild.

With the little parts that came with the carb there looks to be the S shaped tube (broken at the manifold end) that would screw into the choke assembly. I took a pic of what I presume to be the location on the manifold but I'm not sure if it is the location or if the original connection there has been replaced. Would you know if that was the case?

Thanks Tommy

 

[7173Vert]

Do you have the divorced choke mechanism that sits in the well in the intake manifold?

Cliff's book is a good guide for the rebuild. Don't do any of the modifications or "recipes" for improving the operation. Just do a stock rebuild.

With the little parts that came with the carb there looks to be the S shaped tube (broken at the manifold end) that would screw into the choke assembly. I took a pic of what I presume to be the location on the manifold but I'm not sure if it is the location or if the original connection there has been replaced. Would you know if that was the case?

Thanks Tommy

Sorry, I don't quite understand what you are asking about here... Based on your photo, you are missing the dark gray corrugated exhaust gas tubing that goes from the fuel vapor canister to the opening in your air cleaner. If you are talking about the Rochester Carb. Choke pull down assembly, yes, it has been replaced on your car by the recessed cover (held in place by two bolts on the intake manifold). If you are going to use the Factory Rochester Carb. you will need the correct pull down ( I can't be sure what pull down setup applies to your current carb. set up, but I would think you will still need the correct type choke pull down on this engine with your carb.), Unfortunately... the piece you need is both rare and yes, expensive iif you are looking for factory correct... I can take a pic. of mine on my car if you want to go that route. there may be something available aftermarket or through a GM web site that will work if you are not looking for absolute factory correct... For your reference purposes and considering the factory correct piece, when I was looking for mine, there were two on the auction website at that time. The first was a well used one with a firm selling price of $700..., the second was an NOS correct for this engine and Carb. Choke pull down for $295... Guess who hit the "Buy it Now" on that one... Hope I have read your question somewhat correctly...

 

[TommyK]

OK after a bit of cleaning it seems that I don't, in fact, have what would be the original CJ Rochester carb. The number stamped into the body is 17059253 which means it is a 1979 M4MC quadrajet. It is made by Rochester, again stamped on body, and is 800cfm rather than 750cfm. It should have larger primaries as a result. I think that being a post 1975 carb means that it is the modified version, though I don't know what difference that would make. Again, from a bit of reading, it seems these are sometimes regarded as smog era carbs due to very lean fuel metering - would that be true? That's about everything I've found out so far.

I presume it was fitted as a replacement due to some problem with the original quadrajet carb.

Does the fact that I have this modified version of the quadrajet have an impact on trying to rebuild it and put it back on the car? Different rebuild kit I know. Would it have any advantages over the original, smaller quadrajet? Or the holley 3310 I now have on the car?

Thanks once more.

It is a good core to build.

There are three types of Q-jet chokes; divorced choke which is what your car had originally, hot air choke which I believe is what the carb you have now has, and electric choke. The easiest and cheapest way to get a functioning choke is to convert what you have to electric or get another electric choke carb to use.

That carb was originally used on late 70's 350 and 403 equipped Oldsmobiles. Depending on your engine the carb may need to be recalibrated to work properly.

Since the carb isn't the rare and valuable original CJ Q-jet I would stick to the 3310 Holley you have and save yourself some headaches.

 

[mustangandy]

OK after a bit of cleaning it seems that I don't, in fact, have what would be the original CJ Rochester carb. The number stamped into the body is 17059253 which means it is a 1979 M4MC quadrajet. It is made by Rochester, again stamped on body, and is 800cfm rather than 750cfm. It should have larger primaries as a result. I think that being a post 1975 carb means that it is the modified version, though I don't know what difference that would make. Again, from a bit of reading, it seems these are sometimes regarded as smog era carbs due to very lean fuel metering - would that be true? That's about everything I've found out so far.

I presume it was fitted as a replacement due to some problem with the original quadrajet carb.

Does the fact that I have this modified version of the quadrajet have an impact on trying to rebuild it and put it back on the car? Different rebuild kit I know. Would it have any advantages over the original, smaller quadrajet? Or the holley 3310 I now have on the car?

Thanks once more.

It is a good core to build.

There are three types of Q-jet chokes; divorced choke which is what your car had originally, hot air choke which I believe is what the carb you have now has, and electric choke. The easiest and cheapest way to get a functioning choke is to convert what you have to electric or get another electric choke carb to use.

That carb was originally used on late 70's 350 and 403 equipped Oldsmobiles. Depending on your engine the carb may need to be recalibrated to work properly.

Since the carb isn't the rare and valuable original CJ Q-jet I would stick to the 3310 Holley you have and save yourself some headaches.

Yes the 1979 Rochester I have does come with a hot air choke. The stove pipes are broken where they would have entered the inlet manifold unfortunately though. I'd wondered about maybe an electric choke conversion but I read somewhere (another forum I think) that electric chokes don't work so well on older, automatic cars? I don't know why that might be the case. I'll certainly be sticking with the existing holley for now (cold start needs sorting however) but would still like to try and rebuild the quadrajet I have if possible and then do a back to back comparisonwith the holley  before deciding which one to run with.

 

[mustangandy]

Do you have the divorced choke mechanism that sits in the well in the intake manifold?

Cliff's book is a good guide for the rebuild. Don't do any of the modifications or "recipes" for improving the operation. Just do a stock rebuild.

With the little parts that came with the carb there looks to be the S shaped tube (broken at the manifold end) that would screw into the choke assembly. I took a pic of what I presume to be the location on the manifold but I'm not sure if it is the location or if the original connection there has been replaced. Would you know if that was the case?

Thanks Tommy

Sorry, I don't quite understand what you are asking about here... Based on your photo, you are missing the dark gray corrugated exhaust gas tubing that goes from the fuel vapor canister to the opening in your air cleaner. If you are talking about the Rochester Carb. Choke pull down assembly, yes, it has been replaced on your car by the recessed cover (held in place by two bolts on the intake manifold). If you are going to use the Factory Rochester Carb. you will need the correct pull down ( I can't be sure what pull down setup applies to your current carb. set up, but I would think you will still need the correct type choke pull down on this engine with your carb.), Unfortunately... the piece you need is both rare and yes, expensive iif you are looking for factory correct... I can take a pic. of mine on my car if you want to go that route. there may be something available aftermarket or through a GM web site that will work if you are not looking for absolute factory correct... For your reference purposes and considering the factory correct piece, when I was looking for mine, there were two on the auction website at that time. The first was a well used one with a firm selling price of $700..., the second was an NOS correct for this engine and Carb. Choke pull down for $295... Guess who hit the "Buy it Now" on that one... Hope I have read your question somewhat correctly...

Yes I gather the connecting tube from charcoal cannister to the air cleaner is missing, will see if I can find one or try to make something up that will do the job. With the Rochester I have the stove pipe tubes but unfortunately the are broken off where they would enter the inlet manifold. I think I'd have to settle for something that would work rather than try to find NOS at the price it would command. There's always an electric conversion perhaps though I'm not sure how well it would work. If it was no trouble then a pic of what the factory set up is would be great, thank you.