Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Recipe #1 Question

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Tuffnut:
Thanks Cliff, I will give those suggestions a shot.
Jeff

Cliff Ruggles:
Make sure that you use the correct jets.  Most of what's being sold out there is NOT for a Quadrajet.  There are 4 different types of Rochester jets that look the same at a glance but the distance to the orifice varies for each type, as does the angles leading into and out of the restriction..........Cliff

Tuffnut:
1. I was doing some reading last night on the primary power piston hanger adjustment. Since my power piston is non adjustable for a 75, (no APT) just an aneroid,  what would be the measurement I should be looking for?

Remove the rods from the hanger. Sit the piston /hanger assembly upright on a flat surface and measure up to each hanger arm. What distance should should I see from the flat surface to the hanger arm for each side?

2. Also I have used the heavy spring for the primary power piston based on 17" hg at idle. Starts to lift around 2000 rpm under load. Should it lift earlier. I don't want it to be too rich in the cruise.

Jeff

Cliff Ruggles:
The power piston is engine load related (vacuum) not RPM's.  Stronger springs will typically improve throttle response as they have a quicker cut-in point.  With most engines all the springs we sell will be down at idle (lowest engine vacuum), unless you've installed some Thump-Ya-Mutha camshaft in a really low compression engine and are making about 5-7" vacuum at idle.  At that point the best tuning method would be to remove the cam and tink it off the nearest dumpster and put in something better chosen for the application.

If my comments sound a bit sarcastic, well, I really trying to help folks out.  Despite all the great information out there (that we never had back when I got into this hobby) folks still make piss-poor parts selections for these engines.   Not a day goes by I don't get a call from some poor soul wanting a carb or carb work for his engine because it refuses to idle below 1200rpms or so.  Yes, folks are putting 243/257 @ .050" cams on 107LSA's into 350 SBC engines with dished pistons and 882 heads.....then wondering why it doesn't do anything right!

The hanger arms should be level and exactly even on those PP's.

You can do a little custom fine tuning by very carefully raising each rod a few thousanths of an inch, and making them exactly even again, as long as the rod tips stay in the jets at the highest position. 

It's time consuming with those but you'll find you can come up quite a ways on the 44 rods and increase fuel at part throttle without the tips coming out of the jets when it's all the way up......Cliff

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