As much as I hate it, I cannot get my 72 SBC Vette to stop stranding me. The carb runs great up to a certain temp and then .... at a busy intersection....goes full RICH and dies. Requires WOT to re-start and then makes a lot of black smoke. It continues to do this for the rest of the trip. Wasn't sure I was going to get it home yesterday. After it cools off, it runs fine again only to repeat this again.

Where would you buy a good rebuilt Q - Jet??

Over the years I have had POOR results from the discount stores.

How about a Holly rebuilt Q - Jet from Summit ?

Suggestions please > :thumbsup: Thanks!

Napa

Why not contact Sean At SMI. He is one of our sponsors. Discounts for TC members.
He is on the Sponsor list.http://www.camaros.net/sponsors/
I am very satisfied with my restored Rochester from him.:thumbsup:

Have Sean at SMI rebuild your present carb., and save some bucks !

I have a complete, rebuildable Q-jet core available, which happened to come off a sbc Corvette....Let me know if you're interested.....Ron

I just sent an SMI stage 2 Q-Jet back because it ran like crap right out of the box. I tried everything he suggested and it still ran like crap. The idle mixture screws made the RPM's increase when screwed all the way in, the carb made no power at any RPM except off idle, when going to WOT under 2000rpm in high gear(Powerglide) the car fell on its face, and the idle was horrible. Set idle to 850rpm in neutral/650 in drive. After up to operating temp when I would come to a light, I would have to put it in neutral and step on throttle to keep from stalling. He may be better at a standard rebuild, but as far as performance, I am not too sure.

Hey Charlie,

Keep us posted on the outcome.

Recently I posted a carb question with my resto rebuild/mod from sean and The carb was not my problem.

Even though I sprayed carb cleaner around the base, it never made any change with my RPM. So I temporarily replaced the TV cable bracket and paper thin gaskets with a standard gasket and wola! "Vacuum leak"
So now I know where my problem is.
From what I can see it looks like the TV cable bracket I have from Bowtie OD is warped.

I have a Powerglide so no TV cable, but I went over EVERYTHING I could think of and even went over the things Sean suggested and still no luck. Here is something funny. Mat Klemp sent me one of his Q-Jet that he modified like Sean does and from point one the carb ran great. I did notice that on the SMI unit, when I got took the carb out of the box and operated the secondary air valve hold off, if I pushed it in and released it, it just opened up. The carb I got from Mat, when I pushed in the hold off and released it, it made a sort of whistle noise as it was opening up. I thing that the hold off on the SMI unit was bad. I think it was leaking internally. It didn't feel the same when I pushed it in either. It was much looser than Mat's carb. Here is another thing. After installing the SMI carb and having the issues it had, I removed it and reinstalled my Edelbrock Thunder 650 and the car/engine ran GREAT. I did nothing except for swapping the Q-Jet for the Thunder 650, NOTHING AT ALL. That right there tells me that something was wrong with the carb. I swapped the two carbs out numerous times and each time the Q-Jet was on, it ran like crap. As soon as I reinstalled the Edelbrock, BAM, Performance was back. Mat's Q-Jet gave me NONE of the issues that the SMI carb did, but it still was a little sluggish on the top end. I think it is still a little too lean. Q-Jets are extremely lean from the beginning. Mat and Sean richen them up, but I don't think they went rich enough. I am not giving up on my search for a performance Q-Jet. I have 2 cores I am going to rebuild and tweek and go richer with. I think with a richer power circuit I will get what I am after. From the writing on the secondary air valve, it looks like Mat has a 76 jet installed. I am going to go richer than that. First I am going to set it up like Mat, but with a different metering rod and holder.

Why didn't you keep Matt's Q-jet ? Is Sean at SMI sending you a different one ? Bad parts happen. Doesn't mean it can't be fixed. It does sound like someone at SMI dropped the ball. Let Sean, fix the problem. (The carbs. and something to restore the customer's faith !)

Why didn't you keep Matt's Q-jet ? Is Sean at SMI sending you a different one ? Bad parts happen. Doesn't mean it can't be fixed. It does sound like someone at SMI dropped the ball. Let Sean, fix the problem. (The carbs. and something to restore the customer's faith !)


Sean said he wouldn't feel comfortable sending me another carb because he ran it all weekend on his car and he didn't have any problems. I asked him to fix whatever was wrong with it and send it back, but he sent me a refund check instead. I think the secondary air valve vacuum hold off was bad and was leaking. He wouldn't fix it. Instead he sent me a refund. I didn't want the refund, I wanted a Q-Jet that worked and I told him that on numerous occasions. I couldn't have been more clear about my wanting his Q-Jet to work so I could use it, but he wouldn't repair it.
As far as keeping Mat's, I sent him an email asking if he wanted to part with it. I haven't received a response yet. I can understand if he doesn't want to sell it. Either way, I think it will have to be richened up. It feels like it, as well as the one from Sean, was too lean. Q-Jets are extremely lean from the get go. From the reading I have seen, they were an emissions carb and not initially intended for performance. I know they ran them on Camaros, Chevelles, etc, etc, but I mean performance above the norm. Performance that requires jet replacement and circuit modification. I have also read of a modification to the idle mixture screw ports that allows more adjustment. The normal is 3-4 turns out to get a stable idle. This mod allows for 2 or so turns to get a stable idle. Allows for a much richer mixture, if needed. I am not giving up. I WILL HAVE A PERFORMANCE Q-JET IF IT'S THE LAST THING I DO!!! I have 2 cores, but what I really want to know is how they get that nice dichromate finish? How can the average person get that on their Q-Jet?

Strange... about Sean. Have you tried a Jet (brand) Q-jet from Summit ?

Yeah I thought that was odd too. It was like he didn't want to bother with me or something. Honestly, that was the vibe I got. He didn't do too much to try to figure out what was wrong. He just send it back and I'll send you a refund. I have to say that I was not too impressed with my whole experience as far as SMI is concerned. A rather new business and I would think he would try to get all the customers he could and keep them in the process, but I guess not. If it were me, I would have at least had my customer try another carb first. It could have been a fluke. I am sure that Sean does not build EVERY carb that goes out of SMI so I know from personal experience that one can slip through the cracks. Take the carb back, go through it with a fine tooth comb, repair whatever the problem is and send it back and try again. To me, that would have gotten more respect from me than just, "Send the carb back and I'll refund your money". Why not try to fix the problem. If we could have figured it out, then I would have definately gone back to him when I buy a Q-Jet for my 69, but not no way in hell now. Sorry.

No I haven't. I have a feeling that the Jet units are jetted the same as Sean's are. They are quite a bit more money than the SMI unit and if I am still going to have to jet it richer(spend more money), I may just do one myself. I just got the book I ordered, How to Rebuild and Modify Rochesters by Cliff Ruggles. According to this book, I have a 800cfm core sitting in my basement. I think I may rebuild and modify it following the book to the letter. Only I am going to richen it up a bit in the secondaries. The carb Mat lent me felt like it was a little lean.

I think I may rebuild and modify it following the book to the letter.

If you want something done right do it yourself.:thumbsup:

Yeah I thought that was odd too. It was like he didn't want to bother with me or something. Honestly, that was the vibe I got. He didn't do too much to try to figure out what was wrong. He just send it back and I'll send you a refund. I have to say that I was not too impressed with my whole experience as far as SMI is concerned. A rather new business and I would think he would try to get all the customers he could and keep them in the process, but I guess not. If it were me, I would have at least had my customer try another carb first. It could have been a fluke. I am sure that Sean does not build EVERY carb that goes out of SMI so I know from personal experience that one can slip through the cracks. Take the carb back, go through it with a fine tooth comb, repair whatever the problem is and send it back and try again. To me, that would have gotten more respect from me than just, "Send the carb back and I'll refund your money". Why not try to fix the problem. If we could have figured it out, then I would have definately gone back to him when I buy a Q-Jet for my 69, but not no way in hell now. Sorry.

No I haven't. I have a feeling that the Jet units are jetted the same as Sean's are. They are quite a bit more money than the SMI unit and if I am still going to have to jet it richer(spend more money), I may just do one myself. I just got the book I ordered, How to Rebuild and Modify Rochesters by Cliff Ruggles. According to this book, I have a 800cfm core sitting in my basement. I think I may rebuild and modify it following the book to the letter. Only I am going to richen it up a bit in the secondaries. The carb Mat lent me felt like it was a little lean.

Charlie, after hearing your QJ woes, I really think you'd benefit from an A/F meter. I got the Innovate LM-1 and have been messing with my ratio on my QJ. You'll actually have data to make your changes by-You can change your secondary rods in about 2 minutes and get a WOT readout immediately! :thumbsup:

And FWIW, I don't know how SMI jets them but I've got the JET Stage 1 and it's jetted with .073 jets and 41 rods on the primaries and 'DR' rods on the secondaries. The Edelbrock #1910 QJs are .074/50 with 'CE' secondary rods. My original(i think) QJ has.071/45 and 'AN' secondaries. It surprised me but the resulting jet area on the Edelbrock primaries is almost exactly the same as my original.

Charlie, after hearing your QJ woes, I really think you'd benefit from an A/F meter. I got the Innovate LM-1 and have been messing with my ratio on my QJ. You'll actually have data to make your changes by-You can change your secondary rods in about 2 minutes and get a WOT readout immediately! :thumbsup:

And FWIW, I don't know how SMI jets them but I've got the JET Stage 1 and it's jetted with .073 jets and 41 rods on the primaries and 'DR' rods on the secondaries. The Edelbrock #1910 QJs are .074/50 with 'CE' secondary rods. My original(i think) QJ has.071/45 and 'AN' secondaries. It surprised me but the resulting jet area on the Edelbrock primaries is almost exactly the same as my original.

I think you may be right. I think I need an air/fuel meter. They seem to be the way to go to get it dead nuts on.

As far as the SMI unit, I am a little fuzzy with the numbering. Is the higher the number on the jet, the richer it is? .074 is what, the secondary jet size and 50 is what, the primary jet size? What do you mean by AN secondaries? DR rods? 41 rods? I am lost with this. I am used to Edelbrock .101, .098, .095 jets and rods are .073 x .037, .070 x .042, like that. Even the rod hangers on Q-Jets make a difference. This is going to take some getting used to. I just got to the point where I am good with the Edelbrock and now I feel like an idiot all over again.

I think you may be right. I think I need an air/fuel meter. They seem to be the way to go to get it dead nuts on.

As far as the SMI unit, I am a little fuzzy with the numbering. Is the higher the number on the jet, the richer it is? .074 is what, the secondary jet size and 50 is what, the primary jet size? What do you mean by AN secondaries? DR rods? 41 rods? I am lost with this. I am used to Edelbrock .101, .098, .095 jets and rods are .073 x .037, .070 x .042, like that. Even the rod hangers on Q-Jets make a difference. This is going to take some getting used to. I just got to the point where I am good with the Edelbrock and now I feel like an idiot all over again.

Higher jet numbers are richer, higher rod sizes are larger diameter(leaner) but all the late model rods have the same size tip. Therefore, if you are tuning for midrange accel you are on the primaries and primary jet size is the important factor. If your are tuning WOT then secondary rod size is also very important.
On the QJ, you can't change jets on the secondaries- only rods and hangers. The rods use a 2 alpha designation such as "AN" to define the diameter.

I've read this paper about 20 times and it really helps
http://www.florida4x4.com/tech/quadrajet/QJet_Tuning_Paper.doc

Also, this edelbrock tuning stuff is great.
http://www.florida4x4.com/tech/quadrajet/1910

To help answer the original question of this thread, I bought my Jet Stage 1 through Summit because the Edelbrocks had been discontinued. The Ebrocks were the only brand new QJs being offered- all others are rebuilds.

The pros of the Jet as compared to my old QJ are, electric choke, and adjustable part throttle.
I probably could still rebuild the old one and achieve equal performance, but I didn't know much about QJs when I bought the Jet last summer.

Ok so you are saying you can't change the secondary jets? The secondary jets and rods are the ones just in front of the air secondary air valve, right? The secondary rods are the ones exposed, right? Why can't you change the secondary jets? They do come out. So do the primary jets.

Ok so you are saying you can't change the secondary jets? The secondary jets and rods are the ones just in front of the air secondary air valve, right? The secondary rods are the ones exposed, right? Why can't you change the secondary jets? They do come out. So do the primary jets.

I've read nothing about anyone changing secondary jets in a QJ. I've yet to see anyone offering them.

This leads me to believe they don't come out. That, or they are all the same oriface size. Even if they do come out, you'd have to open up the whole carb. The rods can be changed in 2 minutes.

You are correct that the secondary rods are the ones just ahead of the sec air valve (on hangers).

I opened up the carb I have and you are right, the secondary jets, well there not really jets, but orifices that are pressed into the throttle body assembly and they don't come out or get changed. The jets in this carb are 76 and the primary rods are 46k. The secondary rods have DR on them and I can't see anything on the secondary hanger. Mat thinks this carb is a 79 model year. Do they make richer jets than 76 for this model? 76 sounds aweful rich already.

I opened up the carb I have and you are right, the secondary jets, well there not really jets, but orifices that are pressed into the throttle body assembly and they don't come out or get changed. The jets in this carb are 76 and the primary rods are 46k. The secondary rods have DR on them and I can't see anything on the secondary hanger. Mat thinks this carb is a 79 model year. Do they make richer jets than 76 for this model? 76 sounds aweful rich already.

Agreed, the 76/46 sounds much richer than my 73/41. But it is richer at wot and just about the same at cruise, when the rods are down in the jets. Not sure on the DR secondaries but I think they are pretty lean. I believe the same primary jets fit all years of QJ. Primary rods differ, though.

I forgot that the secondary hanger had a "G" on it. Let me try to understand this. This carb has a 76 main jet, you run a 73 main jet, and mine is richer than yours, right? This carb has a 46 primary rod set and yours has a 41, and your rods make your cruise richer than mine because the rods are smaller, right? Why don't you know about the "DR" series secondary rods? Is this series from a different carb? What series do you run?

According to a site I found, ALL secondary jets are .1360" and non removable. This chart shows where in the throttle opening the secondary rods begin their "power" portion of their travel. The "DR" which I have begin at 80* of throttle travel. "CJ, AX and BB" rods start their power portion at 70* of throttle travel. There are more for each style, but there are too many to list. I assume you can use any of the letter designations as long as they are in the same * of travel as what you started with. 70* with 70* and 80* with 80* and 90* with 90*. Here is the website if you are interested:
http://www.thirdgen.org/rods

I forgot that the secondary hanger had a "G" on it. Let me try to understand this. This carb has a 76 main jet, you run a 73 main jet, and mine is richer than yours, right? This carb has a 46 primary rod set and yours has a 41, and your rods make your cruise richer than mine because the rods are smaller, right? Why don't you know about the "DR" series secondary rods? Is this series from a different carb? What series do you run?

The 41 and 46 rods are both 'stepped' rods. Their smallest diameters are equally sized. So at WOT, it's just about the larger jet size. 76>73.

At cruise, you subtract the rod area from the jet oriface area to get the resulting area. They come out about the same. I am referencing the paper by Lars Grimsrud. I don't know the spec of 'DR' secondary rods because he lists them but not their measurement. http://www.florida4x4.com/tech/quadrajet/QJet_Tuning_Paper.doc
My Jet came with 'DR' but I put my old 'AN' in it.

From the charts, i think it's interesting to see how these factory carbs were jetted for their specific applications.

Thanks for the other link.

Here is what the "DR" rod measures from beginning to end:
DR 1323 1250 1093 882 746 581 570 M

Here is what the "AN" measures from beginning to end:
AN 1352 1294 1177 1010 907 797 697 S

It looks like the "DR" is richer all through its travel, right? Am I reading this correctly?

Did you have any issues from going from a rod that begins its rich portion at 80* of throttle travel to one that starts at 90* of throttle travel? I think the "AN" rod is the longer style, isn't it. It would have to be if it starts its rich stage at 90* of throttle travel. That would mean the throttle has to be 90* open and if they were the same length, it would only need 80* of travel, right? These Q-Jets are so confusing. So for the 75-later Q-Jets, the richest primary jet I have found is 77. That is only one more than what it has already. I am used to the Edelbrock where the primary jet runs the primaries and the secondary jet is for the secondaries. On a Q-Jet, it's not like that at all it seems. How do you know when you need to change the hanger?

I bought a book" how to rebuild and modify Rochester Quadajet Carburetors" by Cliff Ruggles and after reading it I found an old Q-jet from a 1985 truck and built my own carb.
All Q-jets are not the same, and can be hard to tune on a modifed engine but this book covers all of that in a way you can understand and use. I followed his recomendtions and my carb works great! and I have about $30.00 invested in it. I would not go back to my old holley for all the tea in China. In my opinion the later Q-jets are the better ones not the older ones. You just have to tune them to work with your engine. My Carb had a factory idle bypass air system all I had to do was drill out a hole a little bigger so it would work with the cam in my 327. This carb is also 850 cfm, more than my engine could ever use but it runs great without loading up or turning the plugs black like my 600 holley used to. I am sure the holley would have worked better if it was tuned correctly also but it was the fuel leaks that really bothered me. I think if I were you I would think about building one yourself first and maybe save some money to.

I am going to do that. I have one that Mat sent me. It has most of the "leg work" done already. It runs good and the off idle performance is GREAT. It just feels a little sluggish at WOT. I am going to change the rods and see what that does. I think if I go to a 527 rod from the current 570. it will wake up quite a bit.

Charlie,
A few posts back you were talking about a place to refinish your carb. The place listed below can do it and is located over on Eastern Ave.. I had a friend take a Holley to them that looked like it had been pulled down the quarter mile behind the car. He said it was perfect when he got it back. He said the total rebuild and replating was like $100. (don't hold me to that). I have copied and pasted from their website.

Carburetor repair Abel Automotive Service has been professionally rebuilding carburetors in Baltimore, Maryland for over 30 years. Carburetors are carefully restored and re-dyed to "like new" condition using premium parts. We also maintain a large inventory of carburetors for sale. Contact us at a1carbshop@yahoo.com or 1-410-288-9400.
Abel Automotive Service
7403 Eastern Ave.
Baltimore, Maryland 21224
We have thousands of cores if your looking for a special carburetor number, Email us with number your looking for, or post the number you are looking for in our guestbook.

Here is link to their website:
http://carburetorsrus.com/

Scott

Scott, that is EXACTLY what I am looking for. That is like 20 minutes from my house. I am going to give them a shout. There is just something about that dichromate finish. I don't know what it is, but I like it more than the Endurashine finish my Edelbrock has. It just seems to match the "cast" finish of my intake much better than the Endurashine finish. Thanks.

Charlie....Glad I could help!

Does anyone know where to buy primary jets, primary rods and secondary rods for Q-Jets? I have been able to find a few, but I went to order one and they said it was unavailable so they cancelled my order.

To the OP, I bought a performance QJet from SMI for my 67 RS/SS350. I am very happy with it. I will buy from Sean again.