Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
1600 rpm idle
F250 Restorer:
17059547. Okay. This is impossible. All 4 throttle plates are seated. All v. ports are capped. Hot air choke passage was plugged. How is this thing getting air and fuel? I close the mix screws to no affect.
This was modified using Cliff's #3 recipe. Mix holes .090. Down angle .053. Float at 1/4". All air bleeds at .070. Jets 73. M.rods 45. Since I converted to electric choke and plugged the v., I added by-pass air of .060 per side to compensate for what it wasn't getting from choke v. I ran this carb w/o the by-pass air drilled, and got the same fast idle.
I don't understand how it is getting fuel and air.
Cliff Ruggles:
What engine? Specs? How much initial timing? Adding timing from the vacuum advance via manifold vacuum?
I've ran into quite a few engine combos that didn't like much timing at idle speed and if you added any with the vacuum advance you lost control of the idle speed.
If all the above is in order you simply have an air leak someplace or the throttle plates aren't fully seated without any light showing. It has to get a LOT of air someplace to idle that fast. If you rule out the carb start looking elsewhere. Gasket under the carb?
I ran into one very similar situation recently on a tractor engine I did a carb for that was burned thru between the exhaust and intake. Did a PERFECT job on the carb and the owner kept throwing it back in my face claiming he checked EVERYTHING else including compression, wires, plugs, timing, etc and it just had to be the carb. Third time he showed up with it I wondered over and helped with the install. Took my a few minutes but I discovered a HUGE hole between the exhaust and intake. Had him buy a new intake instead of a 70 year old junkyard part and ALL the issues went away........
F250 Restorer:
Thanks, Cliff. This is another I6. Ford 300, over-size valves, ported, cam 280adv, .480 lift, 112 lsa. I run 14* base timing. V. advance is plugged for now.
I have a sliver or crack of light around the p. throttle plates. I will try to adjust them. But even with that slight amount of air opening, that is not what would normally pass with the idle adjusted, right? So, as you said, there has to be a leak as well.
"I really like the sound of the engine with those small primaries."
Regarding the forum change: I think that is a good idea about a small charge for your service. However, it may be difficult b/c you are not the one turning the wrench on the QJ's, and the public can be difficult once $ is exchanged. Best of luck.
F250 Restorer:
It dawned on me today that in my infinite wisdom I drilled the baseplate for by-pass air. Tomorrow I will install plugs in the main body of the by-pass passage. Hopefully that will drop the idle.
I checked everywhere for v. leaks. Nothing.
Kenth:
--- Quote from: F250 Restorer on December 15, 2022, 06:04:30 PM ---I added by-pass air of .060 per side to compensate for what it wasn't getting from choke v. I ran this carb w/o the by-pass air drilled, and got the same fast idle.
--- End quote ---
Has to be something else?
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