Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
17059272 on a ford 300
F250 Restorer:
First, I want to say that the last time I used this forum I was really frustrated b/c I could not get my qj to run correctly, and may have spoken badly of a certain qj's mother. It was beyond my skill set. I apologize.
I have since started anew, keeping it all oem. This time around I found a qj from an equal size engine. Now I can get it to idle fine, with 72 primary jets and 52 rods, as it came from GM. But tip in tells me it's lean. I've tried apt thru it's range. So I tried changing to cliff's 44 rods, and couldn't get it to idle. It seems to have great power when floored from a stop. However, when I step on it at 40 mph, it just bogs out and I have nothing. I'm thinking that I have the apt too far out, and rod goes to rich on acc. and gives it too much.
Anyway, this time around I am following Cliff's advice. I'm going to lock out the secondaries and find the best primary jets, then use a rod about 30 diff.
Any help would be appreciated.
I'm not blocking secondaries
Cliff Ruggles:
The metering rods aren't part of the idle system. If you see a change there, the metering rods would have to be a restriction in the jets. Going from 52K to 44's would not be a restriction in the jets, unless the wrong jets are installed in the carburetor and the primary metering rods are too deep.
72 jets and 44 rods in that carburetor are fine, and with the APT system will provide full control of the A/F at part throttle.
Being a 301 carburetor, it has cross drill secondary fuel nozzles, and limited airflap open angle. The secondary throttle plates may also be limited on the open angle.
I would set the throttle plates for full open (90 degrees), install solid fuel nozzles in the airhorn, and grind the stop for the airflap so they come to full opening.
Install a new secondary cam/spring as well.
Most, if not all of the parts from your other rebuild should work on the new carb......Cliff
F250 Restorer:
I installed Cliff's .044 rods. I also went with a slightly stiffer power spring. As Cliff suggested, I adjusted the secondary flaps to open fully, and altered the air flap stop to allow it to open fully. When I started it with the new rods, changed from the oem .052, I could immediately tell the difference. I set the idle and the mix, and there is no longer a bog when I hit the gas at 30-40 getting on the freeway. What a pleasure.
Cliff, why should I change from the cross-drilled secondary nozzles? If it works better, of course I'll do it. I just wanted to know the reasoning behind it.
One question though: I adjusted the mix in till it changes idle, then out to the highest vac. reading. I noticed though, that using the tip-in, it is running a bit lean at idle. I tried to adjust the apt to compensate, but could not. There is also a very slight hesitation transitioning off idle. How can I resolve those issues?
Thank you for the help.
I also have to say that I'm curious why GM would have used the larger bore qj for a 301. Any thought?
Cliff Ruggles:
Fuel distibution is poor from the cross drilled nozzled once you open up the secondary airflaps past the angle the factory set them at.
"Tip in" at idle speed?
The APT is not a player at idle speed, and not used to "compensate" idle fuel requirements.
Idle fuel comes from the idle tubes, then idle down channel restrictions, then to the mixture screws. There are two idle airbleeds in that carb, but the stock sizes for them are fine.
If you need more idle fuel for what you are doing, install larger idle tubes. They are right at .034" in that carb stock from what I can remember. A few thousanths larger and maybe a few thousanths more down channel will help with the lean off idle deal.
The "large bore" q-jet is fine for small cid engines, and they never made any front inlet later style BOP q-jets with the smaller bores anyhow. A few later model Chevy units still used the smaller bores, but disappeared around 1979-80.......Cliff
F250 Restorer:
Thanks for the help, Cliff. I'll be ordering the tubes from you.
kevin.
Navigation
[0] Message Index
[#] Next page
Go to full version