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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by Cadman-iac on November 03, 2025, 06:51:25 PM »
  About the AI information on the Q-Jet, I had to carefully word my questions when I was looking for information, because it definitely refers to the Holley if you don't specifically ask about the Rochester QuadraJet. I had to ask several different ways to get what I did, and I noticed that even if you ask the same question again you get a different answer in that the information is the same but it's formatted differently. Kinda like a kid doing a book report and they change the wording to avoid any appearance of plagiarism, at least that's how I see it anyway.

 As far as if it's correct, I'm not sure. It makes sense, other than the air going through the nozzle air bleed, as I see it, must come through the upper primary air bleeds. The nozzle bleed is buried in the main metering well with the only access being the upper bleed and the fuel well itself, unless I'm missing something somewhere. I would agree with you on this.

 On where the nozzle air bleed exits the main fuel wells, it comes out above the casting that the nozzles are pressed into, just slightly. There is also a very small gap all the around the top half of the nozzle that allows air to flow around/past them.
 I took an old core and practiced drilling and tapping the bleed holes, and yes, I was careful to not go too far, but to resize the hole you do have to go all the way through the casting, but not the actual brass nozzle piece, otherwise you still have a small section with the original size in it yet.

 I have some set screws coming tomorrow as well as a couple of taps. I'm not going to try it on the carb I've got on the truck, not until I'm positive that there's no other way to correct this issue.

 I have been thinking about making the bypass air resizable with drilled set screws, (the base plate has the bypass air going into the short channels on the sides of the primary bores instead of coming out right into the bores so it'll be easier to drill), and maybe making the LIAB holes bigger for the bigger set screws, but I'll have to try it out on a junk core first to be sure it'll work.

 I did run a bigger DCR of .057" and even a .061, but the  .061 didn't change anything.

 Now that I can change things without damaging the carb, I'm going to try different sizes for the UIAB'S, the DCR'S, and see how it responds. If it doesn't work I can go back and try something else.
 I will figure this out, I  may be bald before I do, but I'm not going to quit.

 Not sure how this plays into the equation, but I did remove the POE tubes from the air horn in my effort to make this carburetor match the specs of a Chevrolet carb, with the exception of the nozzle air bleeds.

 I was thinking about it, before I raised the float level, when I ran it without the POE tubes it was running lean throughout the operating range, and when I went up one jet size it improved throughout the range.

 I think they were using the POE system to augment the main system.
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by Cadman-iac on November 03, 2025, 05:53:44 PM »
Just curious... what size fuel inlet (needle seat)?  The Doug Roe book explains that float height and inlet size work together to set the actual fuel height in the bowl.  The lean spot just off idle... is it still a steady state lean spot, or just transition?  If it is transition, maybe try re-seating your accelerator pump check ball?  Look to see if you get a nice pump shot the instant the throttle moves.

 The inlet size is  .130" I think, or  .135", I know it's the biggest one, I got it from Cliff with the kit, so it's getting good fuel flow. The regulator is set at 5.5lbs, and it's rock steady, so there's plenty of fuel available as well.

 By "steady state" if you mean it doesn't suddenly appear and just as quickly disappear but it holds steady at a given rpm range, yes, it's a steady state problem. I can give it throttle and it'll go away when the rpm goes up.

 The accelerator pump definitely gives a good squirt, you can see the AFR go rich immediately, as low as 10.0 before it comes back up to a more normal range, normal being around 13.5-14.5.

 The lean condition is fleeting if you're getting on it, it passes through the range quickly, but if you're steady on the throttle it'll stay in that lean spot until you accelerate past it.
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by novadude on November 03, 2025, 12:04:26 PM »
I finally read through all the AI stuff on bleeds... I think AI is confusing quadrajet with an air-bled nozzle style carb like a Holley.  A lot of what is said there doesn't seem to make sense.  All of the Q-jet bleeds are not bleeding air into the main well below fuel level like a Holley.  I am not super clear on how the relationship between the three main air bleeds works.  Seems to me like you have the upper bleed which is at air horn pressure (atmospheric), the lower main air bleed in the body which would probably be at a lower pressure as air flow increases through the carb. 

Then you have the nozzle bleed which is at venturi pressure.  Since this would be at a lower pressure than the upper main air bleed, it would seem that air would actually flow from the main air bleeds into this bleed and blow into the venturi beside the fuel entering the venturi through the brass nozzle.  Look close... your 0.055 bleed does not actually extend into the brass fuel nozzle, so I'd be very careful trying to reduce this with setscrews. Setscrew would need to be a perfect length so as not to seat on the brass nozzle so that air would still pass through.  I wouldn't attempt it.

Seems like maybe more transfer slot fuel might help... how about a larger IDCR?  I'm trying to recall... did you ever go bigger that 0.046 with your current idle air bleed configuration?  Seems to me that your stock-ish engine shouldn't need it, but that is probably what I'd try next.

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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by novadude on November 03, 2025, 11:39:24 AM »
Just curious... what size fuel inlet (needle seat)?  The Doug Roe book explains that float height and inlet size work together to set the actual fuel height in the bowl.  The lean spot just off idle... is it still a steady state lean spot, or just transition?  If it is transition, maybe try re-seating your accelerator pump check ball?  Look to see if you get a nice pump shot the instant the throttle moves.
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by Cadman-iac on November 03, 2025, 07:00:59 AM »
 Yesterday I was able to work on my carburetor, I raised the float level to 9/32" from 13/32", which did improve the AFR over most of the range, but it still has a lean spot just off-idle.
 The idle mixture screws will change the AFR from extremely lean to extremely rich, and once the engine speed is high enough to pull in the main circuit it runs more on the rich side, it's that transition from idle circuit to main that seems to be the problem.
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by 77cruiser on November 02, 2025, 12:11:38 PM »
You just about like me just had cataracts done in the last couple weeks & yea my hands don't work that great either.
I've read several stories about emulsion bleeds on Holleys, but not  on Qjets.
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by Cadman-iac on November 02, 2025, 08:06:57 AM »
Here's one of the questions I asked online to find out about these nozzle air bleeds.

 How does the main nozzle air bleed differ from the upper and lower main circuit air bleeds on a Rochester QuadraJet and what affect would a larger main nozzle air bleed have on the fuel curve and does having a pull-over enrichment system change the main nozzle air bleed size?

 The previous posts are the resulting answers.
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by Cadman-iac on November 02, 2025, 07:51:34 AM »
 Lol, I wear trifocals, what does that tell you?

 I'd have to buy the drill bit and the tap for something that small. The other problem is just handling things that small.  The arthritis doesn't let me do a lot of little stuff like I used to do.
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by 77cruiser on November 02, 2025, 07:45:42 AM »
You said you only had a phone. I'd never find them on a phone myself. They have 2-56 setscrews too, how good are your eyes?
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Quadrajet Carb Talk and Tips / Re: What are these holes for?
« Last post by Cadman-iac on November 02, 2025, 07:39:09 AM »
Did you try raise the float like Novadude mentioned.
  I haven't done anything with it yet, I've been hijacked into doing stuff for the wife, but I think I'll have a chance to do something with it today.

 Thanks for the link for the 4-40 set screws. I was actually able to find those on my own a bit after posting the question. You just have to know what to enter in the search box, but I'm glad to have a backup in case I can't figure it out.
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