Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
throttle plate v.tubes filled
F250 Restorer:
I am finished with the recalibration. Following Cliff's advice, I opened the idle tubes to 38, the down angle restriction to 52, the mix holes to 95, float level at 1/4", main bleeds are at 70, as is the idle bleed.
I'm anxious to find whether the small primaries deliver a bit more pep off the line. Today I'll toy with the throttle cable bracket and the adapter to a Holley style intake. I'll post my results.
I was a bit lost about which booster spring to use, but went with one that seemed about mid tension. I'll see if that works for the 14hg I have at idle.
F250 Restorer:
I got it running. I was surprised to find that the AFR changed quite a bit from when it was warm in the driveway with the hood up, to when I brought it back after a drive. I attribute that a hot engine compartment and the hood being closed. I went from 12.6 AFR at idle, to 15:1 idling after a drive. I had to readjust the mix screws to get it back to 12.6. I opened the screws and it got back to desired ratio.
But, cool air is denser than hot air. So the engine should go rich with hot air supply, right? not lean?
Also noticed that my test drive was w/o vacuum advance hose connected; carb hose connection capped, hose not connected. I look forward to feeling the difference with the v.a. working, ha ha.
Cliff, how can you tell if the booster is not over-coming the engine vacuum and raising the power piston/m.rods?
Cliff Ruggles:
Engine vacuum falls off WAY below the spring rate with any very quick throttle movements or going to heavy or full throttle. With the later APT carburetors you can remove the plug over the APT and put a cut piece of a drinking straw down over the APT screw and against the pin on the power piston. Move the throttle quickly to reduce engine vacuum and you can see the straw move up so you know it's working.
You can also reach in with a small flat tip screwdriver with the engine not running and push up and down on the pin to make sure the PP isn't stuck or sticking.......Cliff
F250 Restorer:
I just want to say 'thanks' to Cliff for all the help. Had you not written your book, I never would have gotten over my hate of QJ's! Now that I understand it, I would rather have a QJ than a Holley, or any of the other name carbs out there.
I tuned today and found that I had to set the AFR mix for when the hood is closed, not for when it is open. It is funny, when I am sitting in the cab, hood shut, and the electric cooling fan comes on, I can see the AFR fluctuate as cooler air is pulled into the engine bay. Love this carb. I can't wait to dial in the APT for max mpg.
Oh, and Cliff, your specs for the engine/cam were dead on. It purrs.
Cliff Ruggles:
8), I love the in-line 6 engines. They were never all that popular but dead solid reliable and last just about forever. Even cooler to see a 4bbl set-up on one!......
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