Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

'75 Eldorado Q-jet Driver's mix screw no impact

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Benji808:
Hello!

I recently rebuilt my Q-jet (#7045530). First time rebuilder, but it seemed to go smoothly, and the car runs much better, and now starts right up from cold with 1-2 pumps (I think accelerator pump was bad, so that's a big difference - she floats down the road again! I also soaked the disassembled carb in chem dip and replaced carb float.)

Issue(s) I'm still trying to sort out: she idles a bit rough, low, and rich (I've been playing with idle speed and mix screws and it's better, but still feels a tad off)...probably related the driver's side mix screw doesn't seem to have any effect...passenger side shuts the car right down when turned in but driver's doesn't. Also, if I turn the idle screw to a certain point, the engine starts surging - sounds just like someone stepping on and off the gas intermittently. Driving it seems great, but that idle is weird.

I've sprayed carb cleaner around the carb and not finding anything...was going to start replacing vacuum lines, even though they all look fine. What else should I check out?

Cliff Ruggles:
Did you use one of my kits? 

If not did you put a brass float in it?

Were the idle tubes removed or at least cleaned manually so you know they aren't  plugged?

Benji808:
Got the kit from quadrajetparts.com. I did install a brass float, and soaked the metal parts... I did a bit of spraying but perhaps not as much as I could have...internals were pretty clean overall.

After posting I did further testing, and it seems like the throttle body/base plate gasket is leaking (engine rev from carb cleaner spray near the idle screw), so that is hopefully all it is...not exactly sure how I screwed that up but life happens... planning to pull it and install a new gasket today or tomorrow.

The screws worked before the rebuild so I'm not anticipating anything else - main impetus for the rebuild was a bad accelerator pump - but definitely open to any thoughts you have.

Benji808:
Ok...hopefully last question and hopefully you can help me. Take a look at this video (youtube link below). The engine clearly surges when I spray carb cleaner around the idle screw. At first I thought it was the throttle body/base plate gasket, which it could be, but this is now the 3rd gasket I've had on it in the past week. I suppose it's possible I over tightened and crushed it, but I was pretty careful the 3rd time to get a firm torque (tightening in a circle) but not push it.

Am I going crazy? Is there some trick to that gasket? Alternately, the surge seems most consistent right around the idle screw...is there a gasket or something that connects the idle screw to the throttle body? I assumed it was just on the outside, but could be wrong obviously.

https://www.youtube.com/watch?v=h92DhLQ81ug

Attached is a picture of the gasket I'm using (this is one of the old ones I removed...I wasn't overly careful to preserve when I took it off)

Cliff Ruggles:
Never put a brass float in one of these carburetors and most likely you got a "windowed" N/S assembly with a small hole in it. 

Using incorrect parts doesn't help the issues.......

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