Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Tuning for a mopar 318
Cliff Ruggles:
Check the power piston hanger arms to make sure they are level and exactly even. Very critical on that carburetor to have them both at the same depth in the jets.
The big Buick carb also has primary POE, blow some carb cleaner thru the POE tubes and make sure the holes are open behind the choke flap.
That carb has small MAB's, and you should be fine with 72 or 73 main jets for what you are doing. If it continues to act lean even with the APT raised up 4-5 turns, something is fundamentally wrong someplace.
I've build hundreds of those units, and it's rare to have to install large main jets in any of them, at least beyond .073's for a "mild" application.....Cliff
toocheaptosmoke:
Ok, we're back at this. ;D
I checked the height of the power piston arms, they were out about .020" but are even now.
I also installed an A/F ratio gauge.
Here's where it's at right now, I've tried a couple different combos and seem to be going in the right direction. 71 mains, and the dark blue spring from your kit. The stumble I've been having seems to be a lean spot just off idle. Basic rundown is that it runs decent at idle (~14), off idle/light throttle it gets leaner (15-16), then gets rich during heavy throttle. (10-12)
With a vacuum gauge the engine pulls about 15 "Hg at idle. If you crack the throttle a little bit goes up to 20-23 "Hg. You have to crack it fairly quick to drop the vacuum. I previously tried stretching out another spring and was able to get the power piston to move pretty much instantly with cracking the throttle. That seemed to pretty much eliminate the stumble. The blue spring doesn't move until you hit the throttle hard, but I was able to fix most of the stumble by adjusting the APT screw.
toocheaptosmoke:
I went to 70 jets, same results with the stumble a bit more pronounced. I can see the A/F guage hit 16-18 real quick when it stumbles. Still on the rich side during WOT.
Adjusting the APT screw will change the mixture during very light throttle, but it doesn't get rid of the lean spot.
I drilled another hole in the accelerator pump lever to give it more of a shot, that definitely helped but hasn't completely eliminated it.
Cliff Ruggles:
Might want to try closing down the lower idle airbleed some, as they are pretty big on those units from what I can remember.
The accl pump and PP spring are not the problem if you are going lean on light "tip-in", it needs more fuel from the transition circuit and APT system.....Cliff
toocheaptosmoke:
I closed down the lower idle air bleeds, first round I decreased them by about 25% but it didn't do much. Second time I closed them up to a little less than 50% of what they were. Hard to get a good measure, but they were originally around .085" currently around .050", close them all the way?
Stumble still there, that didn't change much. I have unscrewed the APT until the spring no longer held it and it still does it, mixture gets richer just off idle, but as soon as you get into it there's a lean spot.
Here's a video I made over the weekend,
http://youtu.be/vbURvnKEVlM
Really trying to think if there's anything I'm missing here, I appreciate the help and am open to suggestions. Starting to get frustrated, haha. Intake is dual plane, but the spread bore adapter leaves a little gap open between the venturis. I did some research before I put it together and the consensus seemed to be that it was no problem to do that, in some cases even improving hp?
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