Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Trouble with rebuild

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Landshark:
I sent this carb to you a couple of weeks ago to Helicoil the fuel inlet line, great work on that. And we talked and you and I decided that I purchase the the SR kit, 71 jets, 43B rods, gaskets and the red PP spring. I have installed all those parts. I think I just need to back over things and see if an obvious issue is present. I thinking a smaller orifice seat my be worth a try.

Landshark:
I found this procedure out on the web and gave it a shot...Same results....running very rich, black smoke.

So now I'm not sure which way to go with this... ???

How can you tell if your power piston spring is too stiff and not allowing the power piston to “seat” at idle?
If your engine does not produce enough manifold vacuum at idle and/or cruise (due to a lumpy cam or other engine parameters), it is possible that the power piston is not being pulled all the way down to its seated position due to the power piston spring being too stiff. The result is that the car will run very rich at idle, and the idle mixture screws will have little effect or response.  Idle speed may also “float,” with idle speed starting high and gradually decreasing until the engine stalls due to the engine getting “loaded up.”  There will typically be a puff of black smoke out the tailpipes when you “flick” the throttle.

To test for this, pop the top off the carb, remove the power piston/rod assembly, and remove the power piston spring from its bore.  Re-install the rod/piston assembly without the spring and put the carb back together.  The carb will now run in the full-lean condition all the time.  If this clears up the idle, improves idle mixture screw response, and eliminates the black smoke when you flick the throttle, you need to install a softer spring. 

77cruiser:
You can just push it down through the vent & try it.

73ss:
older model carbs like that are prone to the bottom plugs leaking. Check that, It's outlined in the book. If you have a mightyvac you can test the n/s assy for leakage. I like to install the n/s and attach the mightyvac to the fuel inlet. This checks the n/s gasket as well. You have to remove the float or it will hold it open. If everything is good it should hold vacuum for a good 15min or so. You'll have to tear it all down to do this. I didn't have the seat tight enough in mine. Didn't pass the vacuum test. It leaked just enough fuel past the gasket to piss things off.

carmantx:
With that cam, if you didn't modify the idle tubes and down channel restriction, and possibly bypass air, you are going to have idle issues.

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