Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Another APT Question
davis95:
I did a few things that you suggested to me on the phone a few days ago and it runs much better now. I manually lowered the the main rods (bending the arm and then adjusting with the apt screw) and drilled out the mixture-screw holes to .087. The tip-in procedure now works exactly like it should (actually gaining about 200 rpms when partially choking) and the mixture screws respond on 1/4 turns instead of every 2 turns! I didn't remove the idle tubes, but I did ream them out with a piece of wire. I'll pull them on the next rebuild. Response is crisp and clean. It responds to any slight movement of the accelerator pump. I'ts still occasionally (4-5 times a minute) very lightly popping in the mufflers at idle. Is this something that I can completely get rid of or is this just the nature of the beast? I'm really not sure if this is due to a slightly lean or rich condition. As good as it runs I hate to keep adjujsting things, but it would be nice to get it completely smoothed out if possible.
Cliff Ruggles:
Set the idle mixture screws with the engine fully warmed up, for the best idle quality and speed at the leanest setting(s).
Then re-adjust the APT using the tip-in procedure. You should NOT have to do any further adjustments.
If it still has some light "popping" at idle speed, it may be due to too much spark advance......Cliff
davis95:
--- Quote from: Cliff Ruggles on December 22, 2009, 04:30:21 AM ---Set the idle mixture screws with the engine fully warmed up, for the best idle quality and speed at the leanest setting(s).
Then re-adjust the APT using the tip-in procedure. You should NOT have to do any further adjustments.
If it still has some light "popping" at idle speed, it may be due to too much spark advance......Cliff
--- End quote ---
I've been thinking about going with less vacuum advance. Pretty sure you hit the nail on the head with that one. I'm running a 300 HP 350 with my initial timing at 18 and total at 35. Not sure how much vacuum advance it's getting (haven't checked it yet), but pretty sure it's more than it needs. How much vacuum advance do you recommend for this set up?
Cliff Ruggles:
What is the static compression ratio?
How much timing does the vacuum advance add in?
What are the cam specs?......Cliff
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