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The venerable Quadrajet

3K views 8 replies 5 participants last post by  unixsysv 
#1 ·
Hey all, have been reading through the forums before posting but i didnt find a definite answer.... so, here goes.
Problem : 77 vette rough idle in gear only. It will die out without tapping the throttle. Slightly easing up the idle speed or goosing the throttle will keep it running OK. Further, it hesitates, but only ever so slightly on launch.
Will be going through and checking for vacuum leaks yet again in the morning, however, when doing a basic inspection the other day.... i noticed something upsetting. The top and bottom gasket on the carb's main body seems to remain wet with a small amount of fuel leaking constantly. The smell is there but not too strong.
Intake manifold was removed and cleaned a while back, new EGR valve, EFE system is currently disconnected ( vacuum actuator for heat riser had a busted diaphram and apparently no one makes it any more.) No amount of "adjusting idle/mix, fast idle cam, etc " seems to alleviate the issue. Other than the idle speed in gear and mild hesitation problem it runs fine.

I'm thinking of ordering a reman Quadrajet from Summit OR purchase a new Edelbrock EPS 600, but i am concerned about the throttle linkage and such hooking up properly on it.

Thoughts? Carb toasted? Or what?

Thanks for any help you guys can give!
 
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#2 ·
Get the edelbrock, you'll be happy.

A friend of mine tried to get a q-jet to work on the crate motor in his Astro, and we ended up just throwing an Edelbrock Performer on it because we couldn't get the q-jet to stop leaking. Q-jets often will develop leaks along the shafts that the throttle blades sit on, as the housing will wear out of round from the throttle return spring pulling back on the throttle linkage. The only way to fix it is to drill out the housing and put in bushings...

Those vacuum leaks can make the carb impossible to tune, because you simply aren't getting any vacuum signal through the carb. That could be the source of your running problem (we also had a similar problem with the q-jet on his motor, cleared up with the edelbrock)

Now he wishes he would have gotten a squarebore intake in the first place, since it was 15 bucks cheaper, and he wouldn't have had to get the adapter plate...


Chris.
 
#4 ·
the follow up - part 1

Hey all, got some follow up information and some more questions. First, the follow up information -
Couldn't find any major vacuum leaks on the carb. One of the ports for vacuum signal is loose ( stud pulls out of carb with minimal force ) but even blocking this off didn't help the situation.
Removed the air horn and checked for warpage, there is some, while not as bad as some "worst case" photos i've seen, its an issue none-the-less. Secondly, i noticed sediment in the carb where the fuel had pooled up in various areas. Since the day i got the car there was never a filter in the carb body area where one goes. I assumed there was an inline filter elsewhere in the vehicle. I have the assembly manual (from factory) and will see if one is referenced somewhere else on the car.
Now---- On to the follow up questions.
Jmark mentioned, and i have seen a few other people on various forums on the net say not to buy a reman unit. I question, what is the sample rate of "issues" with the reman. 25 out of 100 bad, or more along 1 out of 100? Take JET Reman's for instance, they say that they check proper sizing I would assume the usage of "improper" size's and the such would constitute fraudulent remarks. Basically, what i'm after is, " What is so wrong with a reman from a big supplier/rebuilder " and " What is the sample rate of issues".

It was also mentioned to purchase a new Edelbrock Qjet. This i would love to do. However, going to their new site they no longer list the Qjet. Their old site is still accessible and has it listed there. All retailers list the product as no longer being made. So i say... where oh where can i buy a new Edelbrock Qjet?

Jmark is not the first to call the Performer 600 "boggy". Can you elaborate on exactly what you mean? Also, ideas on how to remove the warpage if a rebuild is decided upon? Any premade tools or such?

Once again, thank you guys for the help.
 
#5 ·
Summit only lists reman Edelbrock q-jet carbs now. They still show new q-jets, but they are listed as unavailable. The thing is, the price of remans is quite a bit higher than a new Performer.

And since performers are based on the old Carter design, they are a heck of a nice carb. One real important thing is that the lower body of the carb is solid aluminum. This helps prevent the carb from warping, whereas other carbs can have the bottom plate warp, and then the gasket there will work. They use metal floats, so you don't have the problem of fuel absorbtion that you do with plastic floats.

And, they are really easy to tune. You can change the metering rods without needing to change any gaskets.

And as for them being 'boggy', I've heard that argument before. That means you need to tune it.

Chris
 
#7 ·
Yet more follow up information

Hey people... lets get to it.
Tore carb off today and tore it down. Main body is warped and was full of debris. Apparently someone before me mangled the carb's fuel inlet. They drilled out the "FI" in the "FILTER" label and installed a screw to lock/retain a fitting adapter for the fuel line. This isnt listed in any manual i own and obviously isnt stock. You can see on the inside of the area where the original threads were but they are severely damaged (never leaked there though). There is a bit of play in the primary throttle shaft, minimal but it's there ( more than the secondaries for comparison which is nil). No filter was/is evident anywhere.

Now, for stock apperance and linkage hook-ups etc... I intend to go with a Qjet. However, as everyone seems to be aware, Edelbrock does not seem to make new units anymore. I would love very much to purchase one of the new Edelbrocks ( anyone have one boxed somewhere, or know someone?) otherwise I'll probably pick up a JET Stage 2 unit.
Here is a nice article about CarCraft having their unit rebuilt by JET.
http://www.carcraft.com/howto/57178/

Thoughts and opinions are welcome. JET or someone else?

Also, here is someone else with the same problem.
http://www.hotrodders.com/forum/qjet-camaro-70418.html

@tattoo3 - yes it's held open. The next major expense planned is to replace the exhaust system anyway with something tame but nice. But, until then if anyone knows of someone with a vacuum actuator for this year, i'd like to purchase it.

I'm going to continue posting information related to this problem in this thread until it is resolved. Perhaps it will help someone in the future.
As i've said before, thanks for the help!
 
#8 ·
As far as the throttle shaft bores being worn, yea, all carbs do it. Personally, i've never had one wear bad enough to cause me idle problems or vac signal problems either. My last qjet went 28 years on my truck and ran fine.

I've had similar luck with Qjets. I find it doesn't matter what carb it is, they will all wear the throttle shaft bores out if the choke isn't working properly. If the choke doesnt close right, most people pump the snot out of the throttle, which prematurely wears out the bores. I've had several come in with a bad enough leak that you couldn't tune it out. Pull the plates, pull the shaft and buy an expensive concentric reamer set so you can install bushings and get the bore aligned.
 
#9 ·
The Long Awaited (or not) Update

Thanks to all who posted and provided help.

As I mentioned I was going to purchase the JET Quadrajet.
Well.... I did, and I must say... the quality is excellent. The instructions were a little lax on one thing, but it's something that is absolutely obvious as you install the carb. (TV cable stud hole position. On the one I recieved, the studs default location was not proper, even after adjusting the cable. Moving it to the second position and readjusting resolved the issue. )

All in all... I'm extremely satisfied with the price/performance/quality of this carb.

Hopefully this information and the above tips from other users will help someone else out.

Thanks again!
 
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