Cliff's Quadrajet Parts and Rebuild Kits

General Category => Quadrajet Carb Talk and Tips => Topic started by: Albert on March 17, 2026, 04:59:32 PM

Title: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Albert on March 17, 2026, 04:59:32 PM

Hi All.
I hope I posted this in the correct place.
I bought Cliff's service kit. His advice, and reading on the forum here has been a God-send!
I have measured all hole sizes in the body and air horn of my current (and first) attempt to restore a this Quadrajet which will go on to a stock standard AMC 304 V8.

Do I need to reduce some holes sizes to suit the 304? The holes in the castings, are larger than what Cliffs First Recipe recommends.

Particularly: Idle channel hole, Upper Idle Air bleed, Accelerator Pump discharge holes, Secondary POE Well restriction, and should I reduce the Secondary Air Flap Opening Distance.

I have highlighted these items in red on the document that I will try to attach below, and a couple of photos of where I am at for now.
First column next to descriptor is my Carby, to the Right is Cliffs recommended First recipe for comparison.

Would it be OK to pop it onto the engine and try run & tune it or will these specs just not work?
I look forward to hearing your thoughts.
Many thanks.

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Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Kenth on March 18, 2026, 02:39:34 AM

You may open the idle channels to .046".
The upper idle air bleeds, .069 are located in the float bowl (not in the air horn) and is on par with Cliff´s rcommendation.
The accelerator pump discharge jets, .026" are located further in thru the outer .060" siphon hole.
The .040" secondary POE well restriction is fine.
The secondary POE discharge jets, .030", are located further in thru the .053" holes. Needs to be opened.
Doesn´t hurt to increase the secondary air valves opening angle.
If you are using an electric choke element and plug the hot air channel, you may want to add some idle bypass air in the throttle plate, .070"-.080" for each bore will do.

HTH

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Albert on March 18, 2026, 06:06:50 PM

NEED to be drilled for the engine to run correctly.

Idle Channel (- Are these also Called Down Channels?) Do I need to open these up, or is it a might need?
Should I try run the engine first, then see if it needs opening?
Upper Idle Air Bleed in Main Body. They are at .069"
Accelerator Pump Discharge Jets are at .026"
Secondary POE Well restriction is actually at .039" - not .040" - will that matter?
Secondary POE discharge jets are at.030" - is this a need to enlarge to .052"? Bearing in mind its only a 304 engine this is going to sit on.
I'll leave air flap distance as is for now, and see how it goes when I run the engine.
If I find I need more Idle Bypass Air, where do I drill the holes, and should they be in the primary throttle plates? (I am using electric choke).

Many questions I know!

Below are my Images to help make sure I have got things right before I start to make "permanent" changes to my Carby.

I look forward to your advice :)

[/list]

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Albert on March 19, 2026, 12:31:09 PM

Hi All.

Thanks again for your initial answer Kenth.

I have confidence in my ability - just not quite there in my knowledge!! :-[
That's why I have popped my question on this forum.
But man - have I learnt a lot in the last month or two!
I am so grateful for everyone that has posted questions, and answers on the various threads before I joined, and that has allowed me to confirm and learn so much before I jumped in to my first QJet restoration. My second will follow in a few months time.

Would it be possible please for confirmation that I have correctly identified the holes, and answers to my current questions, before I start to alter / enlarge any hole sizes?
Images to illustrate my questions are posted earlier in this thread.

I look forward to hearing from you.
Many thanks.
Albert :-\

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: lightning boy on March 19, 2026, 01:18:15 PM

Albert, as far as the bypass air. The milled slots in front of the primary bores are where the bypass air goes. Look Through the main body from the top and you can see the holes that correspond to where you need to drill the base. Don't drill the plates. One channel is straight and the other is doglegged or 90*. Since you have an electric choke, drill them to what Kenth said. It depends on the pcv too.

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Kenth on March 19, 2026, 02:38:13 PM

Albert, i would open the down channel restrictions to .046" to start with.

A picture where the bypass holes enters the manifold.

And a picture where the accelerator pump jets are drilled (thru the "blue" wall).

HTH

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Albert on March 19, 2026, 07:47:27 PM

Many thanks for your prompt reply Gents!
It will be next week before I can get on with the work.
I will let you know how I get on ;)

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Albert on March 29, 2026, 12:50:07 PM

JOB DONE !

...up to this point at least - thanks very much for your advice and guidance Kenth and Lightning boy.

When I read both of your descriptions of the correct location to drill for more by-pass air, I banged my head on a brick wall for a minute :-[ Of course I read about them a number of times in Cliffs book!
I did need your help to locate the accelerator pump jets. I did what my wife would describe as a "boys look", not a proper look!
All holes have now been sized according to your advice, adjustments made according to advice noted in Cliff's book, so, the carby rebuild is done! ;D 8)

The one question remaining in my mind from your comment Lightning Boy, is regards is how the PCV valve is going to effect the running of the engine. It is a very simple straight body valved tube type, connected to the top of the intake with a tube going to the carby. But I am not too concerned about that as I am sure all will be revealed when I do get to start the engine!

I am currently removing the OEM 2 barrel cast intake manifold to pop on an Edelbrock 2131 intake, so I can use the Qjet.
I will post a couple of final images to round this subject off, and once I have the carburetor fitted to the engine, I will be ready to start the engine and start dialing the Qjet in, as far as I can for now.

See you in the "Dialing It In" section of this Forum!

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: lightning boy on March 30, 2026, 05:08:30 AM

Don't over think it. Just see what the factory specified for that engine and try to cross reference one if you have to. It's a controlled vacuum leak, and it's part of the equation, a pcv from a 305 isn't right for a 454 big block in a Corvette. Someone did a deep dive on these once and measured the orifice on each of the part numbered valves for GM that year. Wew!

Title: Re: Bigger holes in Main body and Air Horn than First Recipe recommendation.
Post by: Albert on March 31, 2026, 04:15:55 PM

Well, carby is on the engine now ;D
Lightning Boy, If I find an issue with vaccuum I will see what I can find out regards PCV valve specs. Thank you.
Just need to find a 5/8 x 18 fuel inlet nut to connect the fuel feed pipe / tube on to the filter housing nut, then give the engine a crank and see if my work has been a success!
See you in the dial-it-in pages ;)