General Category > Quadrajet Carb Talk and Tips
cam selection
tayto:
Cliff, opened up the idle tubes .036" and DCR's .052". Surge still there but definitely seems less. I will have a better feel for it tomorrow on my drive to work. Before I took carb off this evening was 14-14.5" hg @ 700 rpm in park. After about the same,maybe moreso 14"hg. Needle still vibrates but only swings about 1/2"hg or less. In gear (600 rpm) only about 13" hg. I figured i'd make more vacuum but i guess its the cam? Idle mixture screws only about 1.5 turns out. I think my APT is 4 or 4.5 turns up. Orange PP spring.
Cliff Ruggles:
You should see more sensitivity from the mixture screws adding some idle fuel.
With some set-ups you may have to close down the lower IAB's some to smooth out idle and get better control with the mixture screws.
I would run it for a for days to see if it likes what you did before making any more changes.
Did you happen to glance into the primary to see if there is any "nozzle drip"?
Advancing the camshaft may also be contributing to the idle deal. I'm not a fan of cams with advanced specs and early intake closing. If you want to tune an engine with "quirky" idle quality fine one with a Comp XE cam in it. I've had so many troubled engines brought up here for idle issues using those cams I hope to never see another one.
Not exactly sure why folks go that direction, but for sure short seat timing, tight LSA and advanced intake lobe positions can make idle tuning difficult in some engines........FWIW.....
tayto:
Cliff, the surge is definitely a lot better after driving it for the last 2 days. It's still there but much more stable and idle seems quieter. Cam was degree'd a 107*, cam card says 108* but it was more like 107.5*. I checked before and didn't see any nozzle drip but will check again. Since the mods my idle screw has been backed up a little. Also found it seems to take off with less throttle idle since mods.
Cliff Ruggles:
That's all telling you likes more fuel to the mixture screws and transfer slots, which most combo's do.....
tayto:
Cliff, what's the next step with closing up the LIABs? Use a check ball to peen them smaller then redrill? Or should I open the idle tubes or DCRs more?
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