General Category > Quadrajet Carb Talk and Tips

Setup Questions

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Chief_Wiggum:
I have a 17059212 that I'm rebuilding with Cliff's book and rebuild kit.  It's going into a full size truck ~6000lbs with a new 350 L31 Vortec truck engine 9.5:1 CR.  No engine mods except 1.6 ratio rockers.  Trans is a 700R4, 37" tires, 4.56 gears.

I'm looking at using Cliff's "First Recipe" as a starting point.  Tore the carb apart, cleaned it and started measuring.

Idle channel: .055"
Upper idle air: .070"
Lower idle air: .067"
Bypass air: .110"

That's as far as I got since the idle channel seems big, and the bypass air seems huge.  Do I need to try and resize these?  If not, what are the implications?  Thanks for the help.

Mike

Shark Racer:
With the idle channel that large I'm sure you'll find that the idle tubes have been enlarged as well. I'd probably go down a bit on them.

Is this the stock truck cam? If so, it's likely very large on bypass air and idle circuit.

Chief_Wiggum:
I already replaced the idle tubes and enlarged them to 0.036" as per the suggestion in the book.  Should I try and resize the idle channels and the bypass air?  What will be the result if I do not?  Thank you for the help.

Mike

Shark Racer:
The idle DCRs will add some fueling to idle. With the idle tubes at 036 it will minimize the effect somewhat. They work as a unison. Not sure how big the effect will be.

Bypass air will make the engine idle higher. You can test it and see if it's a low enough idle. For that motor you could probably idle comfortably between 550-650 rpm.

Chief_Wiggum:
Finally got the carb on and the engine running.  I do have a wide band O2 sensor and gauge.  Unsurprisingly it's running super rich at 10.2:1 at idle and low speed cruise.  I can only get the idle down to ~800 rpm.  The throttle blades are closed all the way. 

Also, the mixture screws are fully seated.  I took the springs off them to make sure.  Where is the carb getting its idle fuel if the mixture screws are closed all the way, the transfer slots?

So it looks like I'm going to need to deal with the down channel restrictions.  Can I buy replacements or am I going to need to make something?  Do they come out just like the idle tubes? 

Is it possible to size the bypass air smaller while I'm in there?  I'm not sure how I would approach that.  Thanks for the info.

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