Just rebuilt a Rochester quadrajet and it runs the engine just fine, BUT, adjusting the mixture screws do absolutely nothing. I can adjust them all the way in, all the way out, or any where in the middle and they dont change anything. If i remember right, that means the idle speed screw is in too far and needs to be backed off some, but i can only back it out so far before its idling too slow and the mixture screws cant compensate..what am i missing here..

You have an internal fuel leak. Is the float too high and your internally spilling gas? A misplaced gasket etc?

Astrobuf

If the carb is OK on the inside as Buf said then the initial is too low

I just had the same problem, when I opened up the q-jet,one of the needles was bent 90* and not going thru the jet.

I must have done that 4 yrs ago when I put a new kit in it, then stored it on the self till last week.

how much slop does the primary throttle shaft have? that can be a vac leak/tuning mightmare. when trying to adjust the idle mixture on a q-jet.

I set the timing with a vac gauge to get highest vac reading, then back off 1 full # and then adjust the idle screws to get highest vac reading while in gear.

what is the part number from the carb?
And what is the application

is there an idle solenoid of just the base adjustment screw?

float levels are super important as stated above.
Also - there is a power piston in the front center of the carb - is it seating correctly?
Kind of is like a power valve on a Holley.

Did you use the same thick gasket under the carb, or did you replace it?
need to be sure it is exactly the same in shape all the way around and particularly up front by the primary bores.

bill

Used to have to epoxy the bottom of the main well feed holes. Between the main body and baseplate.Factory lead pressed in plugs leaked fuel.Even if this isn't the cause of your present problem, it will be a cause of a future one. Usually floods while sitting/draining the bowl.

still have to epoxy -

you are 100% correct about the the fuel bleed down.

the two wells under the jets/metering rods are one source,
the other leak will come from up front where the fuel inlet is.

whats bad is not all epoxies hold up well to ethanol. particularly higher concentrations over 10% for extended periods of time.

I had to send my carb back to the restorer to have him use a marine grade epoxy.