Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: Jeffs68 on September 17, 2016, 04:48:52 PM
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Basics:
Buick 7040244, converted to Pontiac primary linkage, Cliff supplied standard kit, with internals for a Pontiac 400 (stock, 16 heads, headers MSD ignition with an HEI)
Internal parts are:
39B Primary metering rods
Green power piston spring
69 Jets
Secondary rods DA
Float adjusted per Pontiac spec at 1/4 inch.
Installed a Pontiac primary shaft (OEM), so I could use the correct throttle arm, Idles at about 950-1000 Revs.
No vacuum leaks, in fact a quick squirt of carb clean in the throttle body almost stalls it out.
I have full control of idle mixture and have it adjusted.
No drivability issues at all, runs great except for the high idle issue.
Am I missing anything?
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Maybe this does not apply and someone with more experience will chime in, but the carb you have does not have idle air bypass from the factory, and such an engine, even though stock, kind of wants some. I just built a 17057274 for about the same engine and it idles happily with .088 bypass.
Could yours be getting air from let's say the secondary side ? It almost surely is getting air from somewhere. Maybe not from the carb ?
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I'm going to double check things, vacuum leaks specifically.
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I'm going to double check things, vacuum leaks specifically.
No vacuum leaks. I backed the timing down to 12 degrees with advance hooked up to manifold vacuum (without vac advance it's right around 0 degrees). Got the idle down to about 800 and around 700-750 in gear.
As expected, performance has suffered.
Forgot to mention, I do have the base plate APT adjustment available, any chance I have the screw in too far?
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Why not just use ported vacuum so you can put the initial timing back where it needs to be?
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Why not just use ported vacuum so you can put the initial timing back where it needs to be?
I've got a couple other things to look at, that will be one of them this weekend.
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Some engines do NOT like all that timing at idle. Re-set the timing and move the vacuum hose to the advance over to ported vacuum.......Cliff
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Update-
Reset timing to 12-13 degrees, no vacuum advance. Moved to ported source on carb.
Idle is good now.
One other thing about the APT adjustment. On the stock Qjet iron intake (1968) there is the vacuum port smack dab in front of the APT screw...impossible to adjust on the fly.
With the "Tip In" procedure I'm getting a drop in Revs, as opposed to the slight increase. Which way do I turn the screw to get it dialed in?
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With 39B rods and 69 jets you will most likely not have control with the APT system anyhow in that carburetor. I would replace them with larger rods, then employ the APT for fine tuning the part throttle A/F via the APT screw in the baseplate.....Cliff