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Old 04-07-2022, 10:43 PM
71gp 71gp is offline
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Default Replacing original Q-Jet with new Holley 4160 in stock 71 GP

Getting ready to replace the original Rochester Products Quadrajet which has given me nothing but problems. I've had 2 73 GPs and 2 71 GPs, the first 73 being my 1st car I ever bought when I was 17 (40 Years Ago !).
All but one (My 1st 71) had the original Q Jet carbs and all have been problematic due to inherent design defects. Have never been able to get a easy and reliable cold start, which leads to excessive cranking, needing to feed more gas into an already open choke which results in blow-by oil & gas fouling the plugs.
The 1st 71 had a Holley carb, and it ran flawlessly ! On the new 71 I have an HEI ignition which helps keep the plugs clear, but still need to get easy cold starts to avoid the problem altogether. The New Holley 4160 requires use of a 3/4 inch Aluminum adapter plate for the square flange - spread bore intake manifold.
My mechanic has looked at it and questions if their will be any clearance or fitment issues, but still thinks it should fit.
Has anyone using Holley (or Edelbrock) carbs had any clearance issues? Any input would be greatly appreciated.
Thanks

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Old 04-08-2022, 03:13 AM
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You need to find a mech that´s familiar with the Quadrajet.

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Old 04-08-2022, 08:09 AM
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I thought the model 4160 was a spreadbore carb? (or it would be called 4150?)

I've used a spreadbore 4160 Holley on many of my Firebirds. It is close, main problem is the center stud can't be too tall. The GP I would think has plenty of room. (Firebird hoods are really close to engine)

EDIT: I think they were 4165 models for spreadbore. Maybe look for a spreadbore Holley?


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Old 04-08-2022, 08:59 PM
71gp 71gp is offline
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Default Holley 4165 vs 4175

Thanks for your input, Johntal.
I was on the Holley website late last night looking for "direct replacements" for older spread bore carbs like the Q-Jet. Nothing like going back to school to learn about square bore vs spread bore.
Most newer carbs made by Holley or Edelbrock tend to be square bore, but still make a few spread bore units, but none for a Pontiac 400. Companies like SMI or JET Performance offer "rebuilt" Q-Jets for Pontiacs.
I did find a thinner adapter plate (1/8") from Summit Racing vs the 3/4" thick plate I currently have. The bolt patterns on the carb and adapters match, so I'll probably go with that.
Again, thanks for the response.

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Old 04-11-2022, 09:40 AM
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a lot of years ago, i had a '72 and put a holley 750cfm 3310 carb on. used what ever thickness carb adapter was available and a stock dual snorkel air cleaner. no clearance issues at all.
some years ago i put a holley 650cfm spread bore on a '70. it wouldn't bolt directly to the manifold. the fitting screwed into the manifold for the pcv would hit the carb. added a 1" spacer under the carb for clearance and all was good. also with a stock single snorkel air cleaner.

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Old 04-11-2022, 12:03 PM
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I have several quadrajet cars and they all seem to run good. I do have to start them about 3 times before I can pull it out of the garage.

I have three cars with Holley’s on them and the start up and run amazing. Literally flip the key and they will start and idle.

I’m sure the quadrajets CAN run as good, but the wait time for a high end rebuild usually has me opening up a summit catalog unless it’s a high end car.

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Old 04-11-2022, 11:02 PM
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Member, Shaker455 can make your Q-Jet, perfect!

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Old 04-12-2022, 12:09 AM
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The reason a holley can run cold is because most of them are rich, and cover the lean stumble that is common with a stock carb that has an improperly operating choke. Holley doesn't have to make a car run clean as Rochester had to do to satisfy the EPA, etc.

After working with Q jet carbs on my own cars, and customer cars, if all the adjustments are made correctly, they will run like fuel injection. Most times the problem is someone that has either no knowledge of how a Q jet operates, or is ignorant of all the adjustments, and how to make them, has gotten their hands in it, and made it worse. It takes maybe 10 minutes to set all the adjustments on a Q Jet with proper tools. Most people won't make the investment to buy the tools, or take the time to do the adjustments.

On the subject of holley spread bore carbs. I once bought a 70 Judge with one. after a month or two it would be running badly, very rich and dumping fuel out of the venturi clusters. I would take the bowl off, set the float levels (the spread bore holley I had didn't have external float adjustments, requiring float bowl removal), and it would be fine for a month or two. Reset the float levels and again be good for a short period of time. It got old in a hurry, but I would take a Q Jet over a spread bore holley from that experience.

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Old 04-12-2022, 11:59 PM
71gp 71gp is offline
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Default My Status So Far...

Thanks for all the great responses, It's helping me add to my knowledge of all things carburetor related.
I talked with Sean from SMI who was able to impart some great information that has eased "some" of my bad attitude about Q-Jets. Plus, many of you have reported some good results with them. Apparently, getting them properly set up is the key to having them run well. But that's the trick - proper set up in the 1st place....
My concerns about clearance issues (if I go with a Holley 4160) are all manageable. Holley (according to their catalog and application charts) no longer offers any "spread bore" carbs (like 4165 or 4175) for 70's era Pontiac 400s. Just the "square bore" 4160 which I have. They seem to focus mostly on Chevy applications.
So My thinking on this has evolved (with your help) into this:
Plan A: Install the Holley 4160 & related equipment. Being done by very experienced pros at a top-rated shop here in Rochester. Will tweak whatever needs it, and tune it so it won't run too rich and kill my (VERY Expensive) Gas mileage. Yeah, I'll probably have to modify (cut) the original carb to fuel pump line, but heah, that's a catalog item and can be replaced.
Plan B: (Because it always pays to have a Plan B) Save the original Q-Jet that comes off the car (including the dual snorkel air cleaner), and have it "re-manufactured" (Hello, SMI) or replaced with one of their Pontiac appropriate units (335007), which ever works best.
How ever it plays out, feel free to speak up and let me know if you think I'm on the right track.
Thanks again. I look forward to your continued input. I'm going for my degree in carburetors !.
John

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Old 04-13-2022, 12:30 AM
newmexguy newmexguy is offline
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Quote:
Originally Posted by johnta1 View Post
I thought the model 4160 was a spreadbore carb? (or it would be called 4150?)

I've used a spreadbore 4160 Holley on many of my Firebirds. It is close, main problem is the center stud can't be too tall. The GP I would think has plenty of room. (Firebird hoods are really close to engine)

EDIT: I think they were 4165 models for spreadbore. Maybe look for a spreadbore Holley?

Believe 4150 refers to having a pair of metering blocks on either side of main body, with the 4160 is a vacuum secondary type, and has a plate, instead of a block.
Holley did make an aluminum bodied carb in the mid seventies to early eighties, it was the 4010/4011 series. I might have one in stock, but it would have to be gone through, and I would have to think or doubt parts and or gaskets are still available for it.

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Old 04-13-2022, 09:56 PM
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this is the one i put on my stock '70

https://www.summitracing.com/parts/hly-0-80555c

as with any holley carb install, new and rerouted fuel and vacuum lines were needed. once installed and filled with gas, it fired right up with the choke on high idle like it had been on there forever. never adjusted the choke, left it the way it came out of the box. after it warmed up, a small adjustment to the idle speed screw was all it needed. drove very good from idle to part to full throttle. went back and tweeked the idle mix screws, but that didn't make any significant change to the way it performed. could have left them alone. by the way, it didn't need a full 1" spacer to clear the pcv port. probably 3/8" would do it.

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Old 04-29-2022, 08:16 PM
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The Holley will fit no problem. I have a 4150 installed on my '70 GP, and it is mounted on top of an Edelbrock RPM intake (taller than stock) plus a 1" spacer. I run a 3", or maybe a 4", air cleaner element. Hood clearance is not an issue.

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Old 05-06-2022, 07:23 PM
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I'm not an expert but i've rebuilt that exact carb (7041264?) a few times.
Get Cliff's book, give him a call, tell him your combo.
He will send you a turn key, ethanol resistant, kit for your engine.
Your shafts are probably leaky by now. He has a kit & tool for that too.
It's pretty simple to replace the parts.
The holley is "one size fits all"; the Quadrajet was built & calibrated for your engine.
Also there's the choke... I like the "divorced" choke on the '71 quadrajet. mine works GREAT. You'll need to install a manual choke w/ the Holley.
Not a big deal tho.
I think i have an aluminum spread bore adapter around here somewhere...

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