Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
1903 Won't Respond to Tip-In Procedure
bry593:
--- Quote from: Kenth on March 05, 2021, 12:49:39 PM ---I would have stayed with .031" IT and .041" UIAB.
Enlarging the UIAB´s to .052" and IT´s only to .033" will make the blend leaner than the previous. You may need at least .035" IT´s for .052" UIAB´s.
--- End quote ---
I get what you are saying and for grins, calculated the ratio of IT to UIAB areas and assumed a constant .047 DCR.
IT .031, UIAB .042 -> UIAB/IT = 1.8356
IT .033, UIAB .052 -> UIAB/IT = 2.4830, This means the air bleed area is 2.5x larger than the idle tube. So it will pull more air under the same vacuum, but isn't it pulling a greater volume of fuel through the bigger idle tube? I think it results in more fuel and air, but the mix is leaner.
IT .036, UIAB .050 -> UIAB/IT = 1.929, This is Cliff's book recipe and is close to the ratio of .031/.042. Surely this has to pull a larger quantity of both fuel and air through a larger hole (even with the DCR constant). This would suggest idle fuel is greater than .031/.042.
I could be wrong, I have been before....
Carb tip: To set your power piston arms even:
1. Assemble your pp with needles into the carb, but leave out the power piston spring.
2. Set your dial caliper tail on the top of the needle where it bend and enters the arm. Then measure down to the top of the jet.
3. Measure the other side and bend the arm so it matches the previous arm dimension.
This should be darn accurate since it is measuring distance from the needle to the jet.
Pav8427:
Staightening the main body the way you descibed is the way I do it. I built 2 plates that bolt through the carb. Heat till plates are 300ish degrees, snug, cool down, repeat if necessary. Only reason I did was because it was a numbers original carb. Have used it on others and really helped seal things up. I also do the airhorn. Always requires some flat filing to get gooder. The plates I made are machined so I dont have to remove any tubes or parts from the airhorn. Of the few I have done, seems the warp is concentrated at the point where the divider?? plate is in the secondary airvalve bores are. Possibly because the main casting is 'thinest' there.
Doug.
Kenth:
Use of .031" idle tubes with .042" upper idle air bleeds OR .038" idle tubes with .052" upper idle air bleeds, the A/F mixture will be about the same. Your choice.
.033"-.035" with .052" upper idle air bleeds will obviously be leaner.
What counts for you now is to get this idle A/F mixture down to the lower air bleeds and mixture screw needles though the idle down channel restrictions in proper amounts, the A/F blend is fixed.
Larger lower idle air bleeds provides larger amounts of idle/low speed A/F mixture that cures off-idle and low speed issues.
And, even if you measure and bend the arms on power piston there is no guarantee the drilled hole for the rods are at the same spot. Most times they´re not.
Only way to know the rods hangs the same distance is to mount them on the power piston and bend the rod ends towards eachother until they meet at center of power piston end and then adjust the arms if required.
bry593:
I thought it would be best to take the hole in the piston arm completely out of the equation. That's why I suggested measuring from top of the needle to top of the jet. Only two items in this measurement, needle and jet. Being that we are trying to control needle relative to jet, woudn't this be accurate? Maybe I'm missing something?
Cliff Ruggles:
I spend a LOT of time on every carb that I build here to insure that the metering rod hanger arms are level and metering rods are EXACTLY even. I do it like Kenth suggests above, pull them together under the bottom of the piston and make sure the tips are even.
Another good bit of advice is here is to make sure the rods are the same length and that they are the correct length. Not uncommon at all to find the WRONG rods in a carburetor as most have been out there 40-50 years and who knows what has been done to them.
I also recommend putting new jets in them during a rebuild. I find jets all the time that have been drilled out at some point and WAY bigger than they should be.......
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