Quadrajet issue
 

Have a freind with a big block, mildly cammed with a Q-jet that will not idle. Has a rebuilt carb can turn mixture screws in all the way engine still runs, says it's very rich, has completely closed throttle blades then just cracked open, still idles rich. Since the mixture screws seem to have no effect on how it idles can we assume it's bringing in fuel elsewhere? Could the pri. metering be the issue? Been a while since I've even seen a Q-jet, but doesn't it have a piston and hanger that pulls down with vacuum to seat the metering rods? Really can't come up with any other explanation. I've not personally seen the car merely going off what the owner is saying

Re: Quadrajet issue
 

If the cam has a lot of duration it might need a lighter piston spring. what you can do is remove the pri. rods and spring and put in 5 steps leaner pri. jets 67's?, then put just the piston back in.See if that don't clean it up. If it does either nip a coil,or get a lighter PP spring. Most S/SS cars run this way,(without rods).I wouldn't drive it on the street with no rods though.You can also check if the bottom well plugs aren't leaking. gsa612

Re: Quadrajet issue
 

Could just need more idle air. There are a few
Different ways to accomplish this.

Re: Quadrajet issue
 

Ok, yes he's gave it more idle air, that didn't solve it that merely made it idle faster, still rich. The wells have been epoxied, at idle the power piston should be drawn down correct? Pulling the rods into the jets? Looks like I may inherit this buggy so I'm looking for some things to try. Thanks guys.

Re: Quadrajet issue
 

Take a wooden match or small wood skewer
And stick down air vent and on top of primary
Metering rod hanger and mark height to top
Of vent tube, then fire car up and repeat this
Will tell you if the hanger is functioning while
Running.

Re: Quadrajet issue
 

After you do what Ron stated. Disconnect the accel pump, with it running. If it get crisper and idles better, you are rich and vise versa. Dean told me that one, it works. Also you might have to increase the diameter of the passages behind the fuel mixture screws in the baseplate. Example they are .079" open them up to .089". Just a thought.

Robert

Re: Quadrajet issue
 

A trick I have learned the hard way is needle and seat sometimes will leak slightly,but they won't run fuel out vent tube like holley,so it's not as obvious,will drop idle a few hundred rpm,and will bog few feet out because runs over. To check this I remove top and hold float pivot down with finger and put fuel pressure to it fuel level will come up shut off float,then watch for about a minute if leaking fuel level will slowly rise,I have got to where I just go ahead and test all of them I work on.

Another thing to look @ is primary butterflies there is idle circuits that have slotted opening the butterflies have to line up with these slots,adjust idle speed screw to line them up,if engine idles too slow then you have to start drilling holes in butterflies to increase idle speed.

You can also slighly choke w/hand if idles has vacc. leak or blocked idle circuits,too lean,etc
Qjets are more sensitive to vacc leaks,low vacc than holley.
I would also check timing could be retarded too much @ idle.
I would just go over basics first which you'll probaly do first anyway
You can find drinking straws that will fit down vent and push metering rods or watch them operate
Mike Taylor 3601

Re: Quadrajet issue
 

Things I would check:

Fuel pressure - it can't exceed 7psi. If it does, the pressure can blow the needle off of the seat and the carb will flood. Look for fuel dribbling from the booster clusters and listen for irregular "hissing" sound.

Float level - can't be too high, or the carb will dribble fuel into the venturis and the carb will flood.

Secondary hanger and rods - make sure the rods are fully seated in the orifices with the car at idle. The air door must be completely closed (not adjusted to provide additional idle air) because it can pick the rods up and allow secondary fuel.

Make sure the inability to achieve a stable idle is actually due to richness and not simply the result of a vacuum leak. Use the carb cleaner diagnosis method.

Re: Quadrajet issue
 

Is the carburetor rebuilt by a professional, or is it a remanufactured carburetor purchased from a parts store?

Re: Quadrajet issue
 

Heavy float due to absorbed fuel ---Trevor