Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Poor Fuel Mileage on 4.3 V6 with Quadrajet 17056250
don3194:
Are there any detailed articles that explain the tip-in procedure for adjusting the APT? For that matter, where might I be able to find explanations on the proper initial settings for some of the adjustments that exist. Like the choke pull-off, the choke itself, APT, and maybe something else I am missing.
I have found some information floating around but some conflict and plain dont make sense, those did at least get me to a decent running engine with the 17056250, but on this 17059222, I want to have the best chance at getting it absolutely perfect.
Thanks
Cliff Ruggles:
There are "basic" settings listed in the instruction sheets and tech manuals for the choke pull-off, fast idle specs, etc.
Even so it is best to make ALL adjustments on the engine as the factory specs only get you close anyhow.
Here I use a mighty vac pump to apply the choke pull-off and set the open angle to make sure it doesn't choke out or flood the engine. I also adjust the fast idle screw to about 1200-1400rpm's on the highest step of the cam at initial start-up.
The fast idle and curb idles settings can really only be done on the engine with it running. None of this is fussy, but it may take several cold starts to nail down the ideal settings as the engine warms up quickly especially if you have a working exhaust crossover in the intake.......
don3194:
Thanks Cliff. I guess I'm really focused on the APT and I know that can take a lot of trial and error, but is there a procedure called "tip-in" for adjusting APT? I've searched around online and only found people mention it but not explain what it actually is.
Cliff Ruggles:
I just set them at 3.5 turns up from seated for initial testing. Gently "tipping in" the choke from with the engine running around 2000rpm's on the fast idle will tell you if it's rich or lean.
If it's lean the engine will speed up and smooth out slightly. If it's rich it will slow down instead.
That's really all a "tip-in" procedure is. Make sure the engine is fully warmed up and heat soaked when doing this test......
don3194:
Oh okay, thanks for explaining, that makes more sense.
I got it on the vehicle and started it up, at first it was running just fine, I was getting it warmed up to tune it and as soon as I started to reach in and adjust the idle mixture, a nice whistling/sucking sound started, the sound is very clearly heard from down the throat of the carb. It definitely is acting like a vacuum leak(idle is too high, and it responds well to a richer idle mixture), any idea where it could be coming from? When I get the chance to, I'll check my plug for the vacuum to the choke, but I haven't pulled it back off yet to look, but just thought I'd pick your brain for any idea on a sudden vacuum leak.
I did find another baseplate for it, this one actually had bushings put into it and its not worn out. The only reason I'm mentioning this is the possibility that they aren't compatible. The only difference I could note was two extra holes in the "new" baseplate that didn't exist in the original. I circled them in the picture.
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