Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Rich at WOT, lean at idle and cruise
modrummer:
Hey everyone,
I have a quadrajet # 17059219 on my 79 Corvette.
Running #72 jets, .041k rods, and CH secondary rods.
Car has Brodix IK200 heads and a Lunati 268 Cam with longtube headers and side pipes.
I'm running an AEM Wideband 02 gauge for tuning.
Currently, at WOT I have about 11.5:1 A/f (too rich)
However at idle and cruise (once warmed up and choke off) I am getting 16:1 or even higher sometimes A/F (too lean).
What should I be doing to even this out? If I change to bigger primary jets to richen the idle and cruise, my WOT will be WAY to rich.
Thanks
77cruiser:
How far do you have the idle screws out? Do they have any
affect in or out?
When you use a larger than stock cam it lowers the vacuum & usually need some tweaking to the idle circuit.
16-1 at cruise is good if it runs without stumbles or surging.
Cliff Ruggles:
Right to start with 72 jets are really lean in one of those carburetors, and not surprised it's way off the mark on the primary side.
We can supply a much better jet/rod combo for the primary side. Get it dialed in there first, then go after the huge secondaries to tune full throttle.
I'd add here that running 11 something to 1 at WOT isn't really a big deal, better than too lean as EGT's shoot pretty high as does potential for detonation and engine damage.
There really isn't a lot of power gained by playing around with A/F at full throttle anyhow. I've tuned my carb at the track from "pig" rich to so lean the engine was surging just a tad in high gear and the difference in ET and MPH really isn't all that much, seldom much over a tenth and less than 2mph.......FWIW......Cliff
modrummer:
--- Quote from: Cliff Ruggles on May 25, 2018, 10:40:25 AM ---Right to start with 72 jets are really lean in one of those carburetors, and not surprised it's way off the mark on the primary side.
We can supply a much better jet/rod combo for the primary side. Get it dialed in there first, then go after the huge secondaries to tune full throttle.
I'd add here that running 11 something to 1 at WOT isn't really a big deal, better than too lean as EGT's shoot pretty high as does potential for detonation and engine damage.
There really isn't a lot of power gained by playing around with A/F at full throttle anyhow. I've tuned my carb at the track from "pig" rich to so lean the engine was surging just a tad in high gear and the difference in ET and MPH really isn't all that much, seldom much over a tenth and less than 2mph.......FWIW......Cliff
--- End quote ---
Ok so I had some other jets sitting around (74,75. And 78) so I put the 74 jets in.
Measured my float height and its .300" . Checked my piston height and the screw is 4 turns out from bottom.
Went out and drove it to test. Once fully warmed up, idle A/f is about 16:1/17:1.
Cruise and normal driving in gear is right around 12.5:1_13:1.
WOT is the biggest problem. It bogs HARD under Wot And the A/F gauge pegs to 10:1 until it gets higher in the RPM range and then it flattens out around 11:1.
Thoughts?
77cruiser:
Do you have any different secondary rods? Idle could use some work too.
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