As much as I like to keep my 72 all original....I have had enough of the original Q-jet carb. It was rebuilt and runs great, BUT it IDLES so rich it will actually foul the plugs if it idles for more than just a minute or two. Adjusting the 2 screws on the lower front has no effect. Should I just bolt on an Edelbrock 1406 or does anyone have an idea. Someone told me to replace the gasket under the carb. If it leaks it will make it run rich. ????
Any ideas will be appreciated.

 

If your mounting gasket is leaking it will run lean, not rich.
While it is idling, take a look down the throat of the carburetor with a flashlight and see if there is excessive gas dribbling down. Float setting could be off, could have just got some trash under the needle.

 

I copied some portions of Lars' Q-Jet problems list. (I think I found the post on this site a while ago). If the idle screws have no effect, it could be a number of things. I had mine rebuilt as well and am seeing all sorts of problems as well. It just gives us incentive to learn how it really works and to rebuild it ourselves.

Damaged/Leaking Needle/Seat
Results in: Mild to severe flooding and rich-running conditions. Poor idle. Idle mixture screws will be non-responsive. Hard to hot-start.
Comments: It doesn’t take much to cause enough damage to a needle/seat assembly to make it leak: A piece of debris passing through or damaged caused during a previous rebuild process can easily make the assembly leak. Replace the assembly anytime the carb exhibits flooding or fuel control problems.

Incorrect Primary Metering Rods
Results in: Poor idle, rich idle, ineffective idle mixture screws, surging at cruise, poor mileage, poor cold-running characteristics, hesitations off idle and/or at cruise, poor manifold vacuum with resultant ancillary problems.
Comments: See comments for main jetting above.

Incorrect Power Piston Spring
Results in: Poor idle, rich idle, ineffective idle mixture screws, hesitations and stumbles.
Comments: At some time, there must have been a popular article published that told people to cut their power piston springs to hop up their Q-Jet: I see more cut springs that you can imagine. A cut, or soft, spring will keep the power piston seated in the full lean position during part-throttle power, resulting in a sag and poor throttle “feel” during part-throttle acceleration. In contrast, if a stiff spring has been installed, the piston will never seat, and the carb will be running in a full-rich condition even at idle. This causes incredible tuning problems for idle and off-idle performance, and the idle mixture screws will have little effect. New power piston springs are available in packs of 10. If you suspect the spring to be non-original, stick in a new one to eliminate this as a problem.

Hope this helps.

 

[QUOTE=fotyfobravo] As much as I like to keep my 72 all original....I have had enough of the original Q-jet carb. ????
Any ideas will be appreciated.
Here's my suggestion, ( WARNING THIS SUGGESTION MAY CONTAIN MATERIAL FOUND TO BE OFENSIVE TO SOME READERS!)
Find an unmolested 1991 Z28 camaro vin code 8 (I'm not sayin go steal some punk's car) buy a wreck or a something worn out. I started to go into great detail but figured I should condense it so. The idea is to salvage the TPI fuel system, the entire system including distributer and also all the belt driven components, brackets and pulleys and put it on your car. That's the condensed version. Yeah, yeah, yeah I realize it's not all that simple some of you will balk, and yes everything must be cleaned and inspected, and some minor mods will be required.....but.....the end result will be a big ole grin on ya face when ya take it out and blast it. Imagine this, no more setting the choke before cranking and hoping it will start and not die out, flooding it cursing it to start, ruining another starter trying to get it started, replacing spark plugs again trying to start it, sending the carburetor to some slob thinking he even has the faintest idea how to overhaul and adjust a quadrajet, then reinstalling it again and might as well throw in another set o plugs while your at it so you can finally take it around the block praying that it'll make it all the way back home without (don't even think of it goin up in flames and you tryin to smother it with ya tee shirt) stalling. So the latest maiden voyage was a success ah yes the smell of success (smells like a carburetor to me, Eeeek!) Next mornin it don't start. The definition of insanity is doin the same thing over and over, expecting a different result. This is only a suggestion.

 

Other than fouling the plugs at idle how does the engine run? This may give other clues as to what you need to do to fix the problem. How is your ignition system running, is your timing okay?

If you think your power piston spring is the issue this Edelbrock spring set has four different springs -

EDL-1994
Four springs for super-tuning your Quadrajet.
These Edelbrock Quadrajet Power Piston spring kits include four different color-coded springs that will help you fine-tune your Quadrajet carburetor for varying loads and conditions.
Kit contains:
* One 4 in. Hg gold spring
* One 5 in. Hg orange spring
* One 6 in. Hg black spring
* One 8 in. Hg yellow spring

 

It actually juns really good and idles correct. It just idles way to rich. We went to a "drive through" at the local Wendys the other night and about suffocated ourselves and the girl at the window. When I turn both idle jets all the way in....it still idles fine. ??? I think I have a "leak" somewhere out the bottom of the fuel bowl. Seems impossible to find someone that can actually re-build one of these. I am considering an Edelbrock 600 cfm 1406 and just be sure to keep this original on the shelf.
Thanks for the suggestions....etc.....Fred

 

One way to tell if you have a leak - let the car sit overnight and in the morning look through the throttle plates of the carb and see if the bottom of the inside of the intake is wet with gas. Be carefull not to pump the accelerator pump while you do this as it will shoot gas into the intake.

A common problem with QJets is leaking fuel well plugs. The fix is to pull the carb off the engine, drain the gas out and when dry use epoxy to plug the leak(s).

There is a forum member named 'Lars' who is a QJets expert. He rebuilds them so you may want to get in touch with him if you can't find anyone locally who can rebuild it for you or you don't want to try it yourself.

corvettefaq.com carb links

How to tune a QJet by Lars

 

If you're thinking of buying another carb, you might as well TRY to get the $10 rebuild kit from your local shop and rebuild that q-jet yourself. It isn't really a difficult job IMO. I did mine and it ran great for several years before I sold vehicle. Contrary to popular belief, the q-jet is a relatively simple carb with not many parts (choke excluded)

 

is the 1406 a big enough carb for my 383?

it has stock heads and a slightly ratical cam.... (dont remember the specs) I just cant seem to get enough "get" out of it. i have tried nearly every combination of rods, jets and springs. if anybody else has a 1406, what combination are you running?

thanks
scott

 

Someone said to use fuel proof epoxy "somewhere" on the underside of the carb. Does anyone know of this and have specefics??? I like the Q-jet, but it is drowning the 350 at idle. It is a "new rebuilt" CA emissions carb that is correct for the car.

Thanks for any suggestions.

 

If the idle mixture screws have no effect on the idle you may have the throttle blades open too far and the engine is idling on the transfer slot or even activating the main metering system. Check the ignition timing and make sure it is at least 10* BTDC. Retarded timing will force you to open the throttle to keep the engine running at idle. This may be an ignition problem rather than a carburetor problem.

BigBlockk

Later.....

 

I put a 1406 on my car (79) and really like it, especially the price. Just remember, some of the accessories wont line up . For instance, you'll have to buy extra parts to hook up the tranny kickdown as well as the cruise. The tranny kickdown is now gonna be offset and not straight in line with the carb. Plus the fuel line is different, and lets not forget hooking up the electric choke, or manual for that matter. Oh yeah, 1 more thing, no place for the fast idle solenoid for the A/C.
Just my 2 cents.
ESU in NY

 

lars says that most suspected carb problems are actually ignition problems... don't even worry about base timing, take an adjustable timing light and make sure you have 36* total timing by 2800 rpm...