Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Rich at WOT, lean at idle and cruise
modrummer:
--- Quote from: 77cruiser on May 28, 2018, 06:34:22 PM ---What do you have for rods & hanger? Windup on the air valve spring?
--- End quote ---
Rods are CH rods. I'll measure the hanger height, but I believe it is stock height, so if anything I would assume it would need to be bent down a bit to lean out the secondary side.
modrummer:
--- Quote from: Cliff Ruggles on May 29, 2018, 03:58:44 AM ---The idle system is a BIG player here and you need to start there. Idle fuel feeds the main system right off idle and thru transition via the transfer slots, so it is part of the primary side calibration.
Never use used jets and metering rods for custom tuning, they will cause lessons in humility. Always use new parts, if you want accurate results and very, and I mean very fuel jets will pass a pin gauge test and not be worn considerably on the inside from the metering rods being in them for tens of thousands of miles.
Also, K series rods provide very little range of adjustment, we have full tapered rods for that part of the tuning process.
Start with idle tuning, then primary side jet size, then fine tune part throttle A/F with the APT system.
We have the right parts to get you a much better baseline to take a lot of the guesswork out of the equation. This will include jets, metering rods, power piston spring, idle tubes and correct sizes for the DCR's and bypass air.........Cliff
--- End quote ---
Ok I'll work on getting the idle dialed in first.
Both the 41k rods and the 74 jets are pretty much brand new (bought them last year when I was doing some tuning) so that shouldn't be the issue.
So my cruise is currently a bit rich with the 74 jets, but I think that will be dialed in by lowering the primary piston height a little bit. Hopefully drilling out the idle mix screws (or going to bigger idle tubes) will richen up the idle. So the issue I'm left with is the absurdly rich WOT mix (again, it's like 10:1 or richer since the gauge pegs at 10:1). Is a rod change enough to fix that? It seems like the secondary rods couldn't possibly lean out the mix that much, but then again I am not the expert haha.
Cliff Ruggles:
Do you have one of our books?
The idle mixture is calibrated by matching idle tube size, DCR's, bypass air, and idle airbleed sizes for the engine combination.
I would NOT open up the holes under the mixture screw very much on that model as it uses fine pitch metric idle mixture screws and they may not seat if the holes are much larger than about .090".
As mentioned, the primary side calibration is lean for one of those carburetors, assuming it is a large MAB model, which it should be.
With he .118" MAB's most of those carburetors had much larger jets in them than what you are using and they were still extremely lean on the emission calibrated engines they showed up on.
Being too rich with small jets, and rich at WOT with the larger CH metering rods may indicate a fundamental issue someplace........Cliff
modrummer:
--- Quote from: Cliff Ruggles on May 30, 2018, 04:40:52 AM ---Do you have one of our books?
The idle mixture is calibrated by matching idle tube size, DCR's, bypass air, and idle airbleed sizes for the engine combination.
I would NOT open up the holes under the mixture screw very much on that model as it uses fine pitch metric idle mixture screws and they may not seat if the holes are much larger than about .090".
As mentioned, the primary side calibration is lean for one of those carburetors, assuming it is a large MAB model, which it should be.
With he .118" MAB's most of those carburetors had much larger jets in them than what you are using and they were still extremely lean on the emission calibrated engines they showed up on.
Being too rich with small jets, and rich at WOT with the larger CH metering rods may indicate a fundamental issue someplace........Cliff
--- End quote ---
Cliff, interesting point.
I can measure my MABs and see what they check out as.
I'll order one of your books, been meaning to do that.
I'll try to find time to dig into the carb again. It seems like the main issue is on the secondary side, I'm wondering if when I go to WOT the secondaries aren't opening for some reason... the air door opens easily, and the lower butterfly valves open up when the peddle is all the way down so it's not a linkage issue, but maybe a vacuum issue? If the secondary air door doesn't open that would definitely make it go crazy rich at WOT... I may attach a little go pro camera under the hood and run it with the air cleaner off to see if I can see the door opening.
77cruiser:
How long does it take for the pulloff to release from fully pulled in to all the way out?
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