Which Quadrajet to swap ?

[Jesse Jaymes]

I have an Edlebrock carb on my '74. It runs OK on the street, but it is terrible anywhere else. I've read many great things about the Quadrajet on here. I would like to try one, but am lost as to where to start. Can someone give me a few notes so I can start my search? Ebay has several, but the part numbers are very confusing. I have the factory 350 ci, but an Edlebrock intake, which I think is a Performer. As well as ceramic headers with no cats, and straight back on each side. A mild cam is a guess as well.

I am not looking for a monster CFM, but rather reliability and off road performance. At least something to keep me off the key constantly.

I have never rebuilt a carb, but have a fair amount of time, and a need to learn patience. Is it possible to find a carb at a salvage yard and rebuild and learn the ins and outs of the carb and tune it myself and get a better working knowledge. Or buy a new one I know is in working order and have it installed.

Leads me to one more question. There is a plate under the current carb. Will this pose a problem finding the correct plate and pattern for a Q-Jet ? As well as linkage headaches?

 

[bp71k5]

Here's one for a super deal!

http://coloradok5.com/forums/showthread.php?t=231023

You can get a quadrajet adaptor plate for your intake manifold. The plate you have on it probably adapted your existing carb to you intake. It's possible if you have a quadrajet intake, you can toss the plate out. Post some pics of the intake and I can at least tell you if mine would fit.

If you have the performer intake there's a spot where you can hook up a thermal choke element, but I'm not sure what one looks like.

 

[jonrpick]

I have an Edlebrock carb on my '74. It runs OK on the street, but it is terrible anywhere else. I've read many great things about the Quadrajet on here. I would like to try one, but am lost as to where to start. Can someone give me a few notes so I can start my search? Ebay has several, but the part numbers are very confusing. I have the factory 350 ci, but an Edlebrock intake, which I think is a Performer. As well as ceramic headers with no cats, and straight back on each side. A mild cam is a guess as well.

I am not looking for a monster CFM, but rather reliability and off road performance. At least something to keep me off the key constantly.

I have never rebuilt a carb, but have a fair amount of time, and a need to learn patience. Is it possible to find a carb at a salvage yard and rebuild and learn the ins and outs of the carb and tune it myself and get a better working knowledge. Or buy a new one I know is in working order and have it installed.

Leads me to one more question. There is a plate under the current carb. Will this pose a problem finding the correct plate and pattern for a Q-Jet ? As well as linkage headaches?

First off, you say you have an Edelbrock manifold. Is it a dual-pattern manifold that will accept either a spreadbore (Q-Jet) or squarebore (Your Edelbrock) carb? If so, you won't need an adapter.

You mention a "plate" under the carb. Is that an adapter or just a spacer? I had an Edelbrock on my factory Q-Jet manifold and used an adapter to make it happen. You may have the same situation going on.

As to which Q-Jet you need, does your current carb use an electric choke, hot-air choke, divorced, etc??? Look for the same type of choke in a Q-Jet.

My engine was originally the LE9 5.0L/305ci motor. I swapped it for GM 350 crate motor. The original Q-Jet was electronically-controlled (has electrical connections up top). I ditched it in favor of a standard Edelbrock Performer, electric choke/vacuum secondaries. Now I'm about to put on another Q-Jet. The new Q-Jet is an Edelbrock (no longer produced). Electric choke, no other electronic controls.

In terms of rebuilding one, the only hard part I remember from reading up on the process (a while back) was that they tend to wear out along the throttle shaft which leads to leaking. If you have a carb with that problem, the fix is to accurately drill out the hole and install bronze bushings.

If you don't want to do all that, you can buy a rebuilt Q-Jet from Summit that's already had this done. The ones with the Jet brand-name advertise as having had this done. The "house brand" rebuilds from Summit don't. It doesn't mean it hasn't been done, but I was leery about getting one of those since they didn't specify it. The Jet carbs do cost a little more.

The reason I went with the slightly-used Edelbrock Q-Jet is that they were not rebuilds--they were new units. IIRC, they build them a little better than the original Rochesters, so I should get many years of reliable service out of it.

I hope that answered most of your questions.

 

[jonrpick]

Another thing... you asked about linkages.

Your truck would have likely come with a Q-Jet originally, so I would imagine everything should fit just fine. If anything, linkage adapters would have been needed to make your Edelbrock work properly with the factory throttle cable.

Does your truck have a manual or automatic transmission?

 

[Jesse Jaymes]

Brain- I am certainly interested, and willing, but I want to make sure it's what I need.

As far as my carb goes, I looked at the current carb. I can see no electrical wires going to the carb. I have been told it HAS to be an electronic choke, as the only other option is a manual choke, which is a pulled cable from inside the vehicle. I DO NOT HAVE THIS. Again, it's an Edlebrock with a 4 digit number stamped on it. It is not here at work with me today, but from memory it's 1450 or so.

Passenger side of carb does have a round cone or coil though.

As far a the plate vs spacer, I am not sure. It's about 3/4 thick, and the gentleman that worked on my carb prior swapped the one it had out with this one. Was a different configuration internally, and I cannot recall which opening pattern this one has.

I am sorry for the vagueness, but again, I did not grow up turning wrenches. Now in my 30's I have both the time and want-to, so I am starting behind the curve.

 

[jonrpick]

Brain- I am certainly interested, and willing, but I want to make sure it's what I need.

As far as my carb goes, I looked at the current carb. I can see no electrical wires going to the carb. I have been told it HAS to be an electronic choke, as the only other option is a manual choke, which is a pulled cable from inside the vehicle. I DO NOT HAVE THIS. Again, it's an Edlebrock with a 4 digit number stamped on it. It is not here at work with me today, but from memory it's 1450 or so.

Passenger side of carb does have a round cone or coil though.

As far a the plate vs spacer, I am not sure. It's about 3/4 thick, and the gentleman that worked on my carb prior swapped the one it had out with this one. Was a different configuration internally, and I cannot recall which opening pattern this one has.

I am sorry for the vagueness, but again, I did not grow up turning wrenches. Now in my 30's I have both the time and want-to, so I am starting behind the curve.

Probably a 1406. I sold my 1406 just this afternoon... a 1405 is the same basically with a manual choke and slightly bigger jets and smaller metering rods. (ie: more gas for more power).

The 1406 is an incredibly easy carb to work on, but by all accounts, not trail-friendly. There is a kit you can buy for it that'll help make it better on the trail, but probably still not as good as a Q-Jet.

It'd be huge if you could pull it off just enough to see if it's an adapter or just a space underneath there.

You said it has a coil and/or cone on the side... Are there two little metal tabs (electrical connections) on that piece? If so, that's the electric choke. It could've been swapped. Edelbrock does sell alternate chokes for it that can be swapped on. Any hoses going to the choke?

Actually....does the coil have a little "arm" that reaches down and touches the manifold below it?

Don't feel bad. I'm 31 and only really got serious about learning this stuff a few years ago.

 

[Hogback Fabrication]

I am not looking for a monster CFM, but rather reliability and off road performance. At least something to keep me off the key constantly.

You don't need to worry about that with a Q-jet, even though they are rated at 750 or 800 CFM they use small primaries (which is why they work well on V6/L6 engines) but have huge vacuum activated secondaries (that can feed much larger, big block type engines if needed).

I have never rebuilt a carb, but have a fair amount of time, and a need to learn patience. Is it possible to find a carb at a salvage yard and rebuild and learn the ins and outs of the carb and tune it myself and get a better working knowledge.

That's a great attitude. The Quadrajet is probably the best carburetor ever produced, plus its easy/cheap to get and not too difficult to rebuild.

Q-jets were used by GM (and sometimes by Ford, sometimes copied by Dodge) from the mid 60's until the early 90's.

The 60's and 70's Q-jets are probably the best IMO but they didn't use electric chokes. That means you have to use a manual choke (easy and cheap, but you have to work the lever every time you drive) or adapt an electric choke onto an older carb.

Or buy a new one I know is in working order and have it installed.

There is no "bolt on and run" carb, regardless of what the companies tell you. Every carb has to be tuned to an engine.

Lots of people buy a carb that Holley/Edelbrock says will work out of the box on xxx engine. It may technically run the engine but its not tuned right 99% of the time.

Carburetors have to be tuned to match the engine they are powering, there's no avoiding that. If you don't, you're wasting fuel and power.

Leads me to one more question. There is a plate under the current carb. Will this pose a problem finding the correct plate and pattern for a Q-Jet ? As well as linkage headaches?

Your intake manifold is probably drilled for a spreadbore carburetor (i.e. Q-jet) and a previous owner added an adapter plate so that a squarebore carburetor could be installed (i.e. Holley, Edelbrock, basically everything but a Q-jet).

 

[Jesse Jaymes]

Chris

Thank for the response (and everyone else). I've researched production codes and such for the Q-jets, and if I wanted to, I am guessing I could probably find one close to original. But with the mods the vehicle has, I am guessing I do not want an original ?

Thought I'd seen Q-jets offered in 670, 750, and 850 cfm's. Could easily be wrong. I guess I am asking for insight as to which one, or which range of part numbers to begin searching for.

There was a question prior about tranny. It's a TH350 auto.

 

[bp71k5]

Maybe your vehicle is not setup for an electric choke, but there are other choke options. The one mine has is not electric or manual. There's a little arm that goes down from the choke arm and touches the intake manifold. When the intake heats up, the little arm travels up and opens the choke.

I can post a picture of the setup and how it works. It will at least give you an idea of what kinds of carbs in the wrecking yard might work without having to go with a manual choke.

 

[Jesse Jaymes]

The carb it currently has is an Edlebrock 1405 (I had the numbers correct from memory, but wrong order-can dilexia start in the 30's ?)

Website says it's a 600 cfm with manual choke. I buddy of mine who is smart looked at it. You can see the arm where the cable runs from. The vehicle was purchased in Phoenix, and we deduced that with the Africa type heat nearly all year round, the previous owner opted out on the manual cable idea.

Now, I am still looking for which series or range of Q-Jet to look for. According to the smarter buddy, an e choke is nothing more than a wire from carb to somewhere hot, and is about a 10 minute addition.

Sound right ?

Here in southern New Mexico, it is surprisingly cold in the fall and winter. Routinely 17-30 at night from Dec-Feb. So I will need a choke of some type.

 

[bp71k5]

Your buddy's right. The electric choke is just a single wire to a switched ignition source (like the coil) and is probably the neatest option.

I can't help you on the model of carb to look for though. I'd only guess that finding one for a similar year range for your vehicle might be best. I've also heard different people say the "earlier the better" so a 74 might be a good choice.

 

[Hogback Fabrication]

Q-jets are either 750 CFM or 800 CFM. The 800 CFM model generally came on big block cars/trucks, the extra 50 CFM was in the primary butterflies to help with driveability on the bigger engines.

I run the OEM (750 CFM) Q-jet from my truck on my 400+ hp full roller 383. It needed very little jetting change from stock (same metering rods, one size larger jet).

I changed the secondary metering drastically. Each motor has different requirements so I won't bother telling you what I'm using now.

And this carb is basically on a buggy, I've had it at many very extreme angles and its performed VERY well. Better than any carb I've ever been around. It will idle up anything that won't roll the truck over.



The best Q-jets are from the 60's and 70's. All of the carbs from the 60's and 70's used either manual chokes or "hot-air" chokes that used the heat from the intake manifold to determine when the choke opens/closes.

The ones with the APT (adjustable part throttle, 80's) are less desireable because they have electronic emissions controls, but they are the Q-jets that used electronic chokes.




My truck had the "hot-air" choke originally, when I built the motor I had to use an intake manifold that deleted that (vortec heads don't have too many intake manifold options). I used a mechanical choke for a while and then just pulled the choke wide open all the time. When its cold I use the block heater if I can. It works well most of the time.

 

[Jesse Jaymes]

Once again, thanks. I appreciate the patience. Still continuing to look and learn. I stumbled onto a site that had the VIN type break down of Qjet carb manufacture codes. Looks like I will need to re-search that again and find an applicable carb. Also found out about a speed shop in town to swing by and pick the owners brain. I at least want someone available to bail me out if I get into a jam. But I am anxious to attempt it. Again, the idea is to become smarter and less scared about breakage, being able to fix it myself, or at least limp it home without being deserted. I would like to be able to tune the carb, or at least adjust it to the best of my ability. Seems the Qjet handbook for $24 is the best place to start after getting a carb. The Ebay rebuilt ones look aweful clean and nice, and ready to bolt on an go for $190. But I can't help but believe there are many applicable Qjets sitting around the salvage yards that are almost being given away.

 

[dyeager535]

Just a minor correction...only vehicles that across the board got electronic Q-jets were cars from 1981+. The ONLY trucks that got electronic carbs were the ones that went to California. Truck carbs up to and including 1986 are most likely to have a "standard" Q-jet, although the carb is tuned for EGR, EVAP, etc. It has more vacuum ports on it than prior versions, but on an older vehicle, you'd simply cap or plug them.

 

[jonrpick]

Just a minor correction...only vehicles that across the board got electronic Q-jets were cars from 1981+. The ONLY trucks that got electronic carbs were the ones that went to California. Truck carbs up to and including 1986 are most likely to have a "standard" Q-jet, although the carb is tuned for EGR, EVAP, etc. It has more vacuum ports on it than prior versions, but on an older vehicle, you'd simply cap or plug them.

You raise an interesting point Dorian...

My truck is an '86, yet had the electronically controlled carb with the LE9 (5.0L) engine, but was not a California truck. It was a Police truck from TN. When I got the factory wiring manual for 1986, I couldn't find my exact configuration in there. Do you think there were exceptions to the rule for government vehicles?

 

[dyeager535]

I saw your other post, I would be VERY surprised if yours was computer controlled. It would be atypical for anything "one off" from GM to have more stringent emissions, it's almost universally the other way around...it kept cost and complexity down.

CCC (computer command control) had an ECM mounted under the dash, right where the TBI ECM is mounted. If it didn't have that ECM, then it wasn't CCC. Now keep in mind GM ran *ESC* (also called EST) with the 305's due to their high compression and being prone to detonate on 87...that just allowed the distributor to retard timing, and had nothing to do with the carb, but did have a small control box under the dash in the same location that is commonly mistaken as an ECM.

Another identification of a CCC carb is that the DRIVERS side front of the carb will have a three wire plug on it, which is TPS. No carb but CCC got TPS.

I suspect I know exactly what you had, it was the dual capacity solenoid, which had to do with cold engine running and additional enrichment during that period. GM also could have tacked another component onto the dual capacity solenoid, as there can be two connectors off that same location, but I can't recall what it was.

The non-CCC truck carbs with electric parts all have the connector on the front, top passenger side.

 

[jonrpick]

I saw your other post, I would be VERY surprised if yours was computer controlled. It would be atypical for anything "one off" from GM to have more stringent emissions, it's almost universally the other way around...it kept cost and complexity down.

CCC (computer command control) had an ECM mounted under the dash, right where the TBI ECM is mounted. If it didn't have that ECM, then it wasn't CCC. Now keep in mind GM ran *ESC* (also called EST) with the 305's due to their high compression and being prone to detonate on 87...that just allowed the distributor to retard timing, and had nothing to do with the carb, but did have a small control box under the dash in the same location that is commonly mistaken as an ECM.

Another identification of a CCC carb is that the DRIVERS side front of the carb will have a three wire plug on it, which is TPS. No carb but CCC got TPS.

I suspect I know exactly what you had, it was the dual capacity solenoid, which had to do with cold engine running and additional enrichment during that period. GM also could have tacked another component onto the dual capacity solenoid, as there can be two connectors off that same location, but I can't recall what it was.

The non-CCC truck carbs with electric parts all have the connector on the front, top passenger side.

I'll look at that carb again. It definitely had the ESC (now disconnected since moving to the 350). You're probably 100% right. I just found it strange that the closest thing I could find, wiring-wise, in the manual was a California V6.

It's been 2 years, so maybe I missed something, but I'll look again.

 

[dyeager535]

In all my parts hunting, I've never run across one of the truck carbs with the "partial" electronics on it, so even on this site you'll see people calling them computer controlled simply because they aren't well known. Heck, I had people on a car board not believing me, until I posted the GM parts manual scans from the truck showing that specific carb.

I assume on the dual capacity pump carbs you can simply leave it disconnected and re-tune it, but I've never had one apart to figure out exactly how they work.

 

[Mike D]

Why not contact Edlebrock and get a rebuilding proceedure as well as information to custom tune that carb to your engine. A good Q - jet will cost about $ 350. A worn out one will cost $ 50 - 150. plus $ 50 for the rebuild kit, assuming the throttle bushings aren't worn out. At 5000 RPM a 350 cu. in. naturally asperated engine will suck in 450 CFM of air. Any carb greater than 600 - 650 CFM will be too much.

Many years ago Holly offered a 450 CFM carb to replace the factory Q jet. I bolted it to my 68 Impala ( 327 cu. in. 4 speed ) After adjusting the carb settings ( mostly trial and error ) I had a 3500 pound car that had crisp throttle response ( no bogging ) 4 more MPG and could out accelerate most Cameros.

 

[jonrpick]

Why not contact Edlebrock and get a rebuilding proceedure as well as information to custom tune that carb to your engine. A good Q - jet will cost about $ 350. A worn out one will cost $ 50 - 150. plus $ 50 for the rebuild kit, assuming the throttle bushings aren't worn out. At 5000 RPM a 350 cu. in. naturally asperated engine will suck in 450 CFM of air. Any carb greater than 600 - 650 CFM will be too much.

Many years ago Holly offered a 450 CFM carb to replace the factory Q jet. I bolted it to my 68 Impala ( 327 cu. in. 4 speed ) After adjusting the carb settings ( mostly trial and error ) I had a 3500 pound car that had crisp throttle response ( no bogging ) 4 more MPG and could out accelerate most Cameros.

I forgot about that... Holley still does offer a spreadbore Q-Jet replacement. It's not a true Q-Jet, but will bolt right up. Plus it'll be new.

According to the newest Summit catalog in my hands right now, it's a 650CFM carb, with electric choke and vacuum secondaries, for $363.95.