Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Idle problem
Cliff Ruggles:
Impossible to read plugs on this new fuel.
Always tune for best results. If it needs more fuel the engine will tell you. Start with idle, set the mixture screws for best idle quality and highest vacuum a the leanest settings.
Test heavy part throttle next, and dial in the jet size which provides the best power at heavy part throttle, climbing up steep grades, passing w/o the secondaries, etc.
Then tune the part throttle for best off idle at light throttle openings, steady cruising, etc.
Last tune full throttle with the secondary metering rods.....Cliff
dlphil10:
Good to know, thank you for confirming spark plug reading is difficult. The plugs look white, but more gas makes the idle unstable and causes it to be a little shaky. I know I need to get my advance curve coming in faster, but I think it still needs more gas in part throttle.
If I ease into the gas it'll do good, but it bogs with part throttle stabs. Heavy part throttle seems good (~5-7inhg). I'm thinking this would be helped by changing the power piston since this lines up with the orange spring that I have. If my drive idle vac is 13.5in hg. Would it be ok to use the stiffest spring? I have the long green, orange, and small light blue spring that is shorter than the green. I belive it came wth the plain spring, but it was lost.
Cliff Ruggles:
Yes, you can use any of the springs for fine tuning they will all be down with that much vacuum at idle.....Cliff
dlphil10:
Awesome. I know there are two light blue springs in the kit, is there a length difference between the weak one and strong one? The one I have is shorter than the green spring.
Would the power piston spring be the first thing to change for part throttle tuning, or should I be look into fattening up the idle circuit to free up more of my transition slots?
Cliff Ruggles:
The power piston will be down for most light throttle/normal driving. You can increase fuel to the main system by adding idle fuel with larger idle tubes/DCR's. This can help with transition issues and being too lean right off idle as well. Just be very conservative when tuning in that area as it does increase fuel to the mixture screws and exposed transfer slots at idle and you can put too much fuel there and loose control of idle A/F with the mixture screws......Cliff
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