Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

idle bypass question

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wannabemachinist:
Thanks for the reply. I guess that could be a k on the metering rods. I read in other posts that k's are not that good for tuning purposes. Would you have a jet / combo that you would recommend?
 I am having a hard time making myself clear about the main air bleeds. There are 3 orfices in each throttle bore 2 at the top and 1 in the lower part of each throttle bore which I guess is the IAB that you refer too
I realize the cam is mild but for daily driving it seems fine at this time and the car is quite responsive as it is set up but I am looking to be able to have adjustment on the air fuel adjustment
 So dealing with cards I have could you recommend something that could help my issue

Cliff Ruggles:
Address the idle issue first.  Take a gander into the carburetor at idle and verify that there is no fuel dribbling from the boosters.

If not you may already have enough idle fuel but lack control of it because too much transfer slot is exposed.

Remove the carburetor and turn it over (make sure the stop is against the idle speed screws) and see how much transfer slot is exposed.  If you see a lot of transfer slot exposed adding bypass air will lower the throttle angle and degrease the amount of idle fuel it's getting there and may restore some response to the idle mixture screws.

Before you do that I would however back the idle screws out quite a few turns and see if it goes way rich at idle, indicating that at least you have plenty of idle fuel right to start with.

I would also full seat the idle screws (remove the springs from them since you opened up the holes under them) and see if you have any control at all of idle fuel at or close to seated.  If you see some control doing this (engine slows down) and no nozzle drip then your idle tuning may be over.

I've tuned a good many engines brought here using that particular camshaft and not overly impressed with it.  Idle was "quirky" and although it throws some power at you right off idle and initially "feels" pretty responsive it's not overly impressive otherwise and how could it be as it's 12 degrees less seat timing that a stock replacement cam and tighter LSA......FWIW......Cliff

wannabemachinist:
I checked  the carb today as you suggested and found no dribbling from the boosters
Backed out the adjusting screws, the idle became slightly worse
Turned the idle screws completely in and pretty much stopped the motor
Removed the carb and checked the transfer slot. It was exposed close to 3/32 or .092 and when the idle speed screw was backed off completely it was exposed slightly over 1/32
My idle screws are backed out about 2 1/2 turns and showing about 15 inches of vacuum at about 725 RPM
Initially I felt I was not getting anything when turning the screws in, even with a coil removed from the spring but today I did. Definitely not a huge change when backing them out though
When it starts cold and the choke is on and I completely close the flap it will die if left
Could all this be improved upon? (besides the cam at this point :))
You mentioned the jets and rod being lean also. What would you recommend
Thanks

Cliff Ruggles:
If you have control of the idle fuel from rich to lean and no nozzle drip I'd leave that alone.

Does it work OK otherwise?  Do some testing at light part throttle and heavy part throttle to see if it needs more fuel in those areas?...Cliff

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