What's the best place to buy a Q-Jet for an economy application? I have a bone-stock 350 in my 64 C10, and would like to swap out the Holley 4BBL for something more economical. I'm really not knowledgable enough on carbs to buy a core and rebuild it. I've heard the replacement QJets available through AutoZone, etc are junk. Are the Edelbrock QJets available through Summit any good? Anyone have a better idea? Thanks for any advice.

Holley makes the very best stock rebuilt Q's. There are also others advertised here. Sean Murphy also comes to mind.

I don't personally like the Edelbrock Q's. You may have good luck with them. They are made by Weber USA. I had a new GM Quadrajet from the same source (1997 build) and it had a few problems out of the box. The most significant was that the idle air bypass holes were not drilled. Not an easy problem to remedy at home.

Anyway, very best luck to you.

Mike

I didn't realize that Holley was re-manufacturing QJets, thanks for the tip.

i'd buy the Holley with Q-Jet base plate.

Mike,
If you have (or can find) a good Q-jet core, send it off to Lars in CO for rebuild/mod. I did that with the Q-jet on my wagon...came back spot on! :thumbsup:
You'll need to supply all the specs for your application. Turn time was one week.

You can get or tune some Holleys into the 20 mpg range on a v8.

One of my toys has a Holley 8005 (an emission style carb, 600 cfm, vacuum secondary, reverse idle) that will get 21 mpg on the interstate with 273 gears and no o/d. It has close limit jets, and a 2 stage power valve.

I will admit that I also swap it with an 80457 that gets 14 mpg, but I have not done any economy tuning to it, mostly the opposite tuning.

To get much better than 15 or so, I think you will have to tune almost any carb. I have not fooled with the Edelbrock 1406 on my Chevelle. It's run ok, and I have not checked mileage. I know more about Holleys, and I want to go efi, and not learn the intracies of any more carbs. (Got burned out on Mazda Nikki staged, electronic feedback, 2 barrels, but I can make them work!)

Q jets have a good reputation for economy, but to me, they are more complicated to adjust. I would go with one of the smaller Holleys.

Mike,
If you have (or can find) a good Q-jet core, send it off to Lars in CO for rebuild/mod. I did that with the Q-jet on my wagon...came back spot on! :thumbsup:
You'll need to supply all the specs for your application. Turn time was one week.

I've got a couple of Q-Jet cores, but I'm not sure they would qualify as "good." I'll get with you sometime on contact info for Lars, maybe I'll get lucky on one of my cores.

Here are a couple of extra points about Q-Jets:

In shopping for Q-Jets, better to get a later model than an early casting. The late models have an adjustable feature to fine tune the fuel curve that is accessible and tuneable even with the engine on and running. The screw adjuster is located in a well which is plugged by an aluminum "cork" which is located on the top casting underneath the air cleaner gasket ring area, directly in front of the choke housing. You remove the plug (no big deal), tune and adjust over a period of time, and when you're happy just replace the plug and you're finished. You can drill and tap the "cork" to make it removable whenever you wish with no work at all.
The early versions have the same feature but it is located behind a driven-in hard plug in the baseplate. These are only adjustable with the carb off the engine, meaning a lot of "cut and paste" tuning. Much more difficult than tuning with the engine running.

For anyone not very familiar with carbs, especially Q-Jets, I'm not referring to the idle mixture screws present in the baseplate.

This adjustment acts to control the depth of the power piston as it returns to idle position, and can be used to increase gas mileage at very low speeds and idle, essentially cleaning up high vacuum fuel delivery situations (over about 16-18" vacuum). The power piston controls the needles which insert into the jets, and thereby determine the entire running fuel curve of the primary side of the Q-Jet carb. Jets play a role in tuning these carbs, but not like you think of jets when tuning a Holley. The needles are critical, but easy to understand, and the adjustment I'm talking about is a way to fine-tune these.

Just for fun, the secondary side of the Q-Jet does not have replaceable jets, and the mixture strength is also controlled by tapered needles which are inserted into the jets and rise and fall according to engine demand.

The taper of the primary and secondary needles is very important in tuning and proper operation.
In this way, the Q-Jet, which is one of the most sophisticated carburetors ever made (GM spent 4 million 1962 dollars designing it) is very similar to another outstanding carburetor, the SU from Britain.

There are basically two Q-Jet sizes... a 750 cfm used in almost all applications, and an appx 800 cfm used for the big Caddy engines of the early 70s. They are easy to tell apart, and the Caddy has the same 90 degree fuel inlet position required on Chev engines.

There is also a less well known version of the Q-Jet which has an "altitude compensator" that senses air pressure (altitude) and adjusts the fuel curve correspondingly.

These carbs can deliver great power and excellent mileage. The only real drawback to the Q-Jet is the erratic fuel delivery curve (full of spikes and depressions), but so long as you keep the fuel bowl supplied, in most instances the Q-Jet works fine as a performance carb. In the early 70s it was common to see stockers at the drags running in the tens with a 396 and a Q-Jet.

Quadrajets these days (real GM ones, now with a lot of miles on them) will almost always have to have the primary throttle shaft rebushed. Failing to do this will result in a carb that cannot be fine tuned. It is pretty easy to do, but you must have the proper tool and knowledge of dealing with throttle butterfly screws to do this safely. It is very easy to ruin a Q's primary throttle shaft. This is best left to a carb shop unless you do have the proper ream and brass tubing. The throttle butterfly screws can kill you on the highway... no kidding... if one or more should fail after a throttle shaft ream job. Working with these tiny screws is probably the most important part of the carb safety issues, and as I said the throttle shaft and baseplate can be ruined if these screws are not dealt with properly.

In the 300+ Quadrajets I've built for other people over the years, the only real issues I've seen concerning the quality of metal chemistry are with the ones built on contract to GM by Carter (yep, the AFB people). These carbs were built by Carter, at their assembly facilities. The zinc alloy used is more fragile and corrodes much more extensively than the GM produced carbs do. Of the numerous Carter versions which have come before me, only about 15% were rebuildable. Any Carter stored outside (junkyard, parts pile, etc) for any length of time is likely junk. You can spot these carbs easily... Carter put thier name right on the main body casting... just read it.

Eric

What's the best place to buy a Q-Jet for an economy application? I have a bone-stock 350 in my 64 C10, and would like to swap out the Holley 4BBL for something more economical.

Mike,

It's hard to beat a well tuned Q-Jet on a mild street small block, especially if you are wanting half-way decent MPG.

If it were me I'd contact Sean at SMI and have him do his "Magic" to one. He will total go through the carb and "tune it" specifically to your vehicle / setup.

I had Sean do Stage 1 mods on a Q-jet for my daily driver 84 C20 Suburban. No problems at all. Drives great! Give him a call, his price is very reasonable. The prices on his website is with him providing a carb. It is cheaper if you use your own.


http://www.smicarburetor.com/products/?sfID1=28&sfID2=9&sfID3=32

Thanks everyone for the ideas, I'll see what I can turn up.