69 Big Block Carburetor Decision

[Chris L.]

I have a 1969 427 (bored 0.03" I believe) 4-speed which I acquired last fall and needs the carburetor rebuilt or replaced. It starts and runs fine at low RPMs, but has significant hesitation upon acceleration. I am considering a rebuild kit or replacement. While I have done some carburetor work on other cars, I know the intricacies of carburetor work and am leaning towards a replacement.

I do know the current Quadrajet is not the original. It was replaced in the 80's due to a botched fuel filter replacement attempt (I am guessing as the fuel lines are crimped and twisted a bit). Therefore, I am more OK with replacing it as it was not the "original".

If I do pursue a replacement, I am wondering if I need to upgrade the size to accommodate the larger displacement. I am told a 427 bored 0.03" is 454 cu in?

Any advise on this would be appreciated.

[Dick W.]

Re: 69 Big Block Carburetor Decision

427 bored 030 is not 454. You need a little more stroke to achieve that. You are about 433 or 434 cu in.

You can get a rebuilt carb from your local parts house, find one the the NCRS, Driveline, or go junking.

Hesitations such as you are talking about can be caused by the secondaries opeing too quick. Get a shop manual and try adjusting the secondaries before you replace the carb.

[Joe L.]

Re: 69 Big Block Carburetor Decision

I have a 1969 427 (bored 0.03" I believe) 4-speed which I acquired last fall and needs the carburetor rebuilt or replaced. It starts and runs fine at low RPMs, but has significant hesitation upon acceleration. I am considering a rebuild kit or replacement. While I have done some carburetor work on other cars, I know the intricacies of carburetor work and am leaning towards a replacement.

I do know the current Quadrajet is not the original. It was replaced in the 80's due to a botched fuel filter replacement attempt (I am guessing as the fuel lines are crimped and twisted a bit). Therefore, I am more OK with replacing it as it was not the "original".

If I do pursue a replacement, I am wondering if I need to upgrade the size to accommodate the larger displacement. I am told a 427 bored 0.03" is 454 cu in?

Any advise on this would be appreciated.

Chris------


The vast majority of Q-Jets are in the range of 750-850 CFM. You won't need more than that for a 427 or a 454 (or, even a 502) used for street applications.

[Don W.]

Re: 69 Big Block Carburetor Decision

Hi Chris,

I also have a 69 427 390 HP with a non-original quadrajet. If you want to try and find a correct numbered carb expect to pay $1,000+. I bought a aftermarket service replacement for summit racing. Then, the car had to run on a dyno and the carb re-jetted to get optimum performance. After about 6 months, float developed a pin hole and had to be replaced. So it's a long process to get things sorted out. That version of the quadrajet has many sizes of primary and secondary jets available.

Don

Here's a summary:
I have a '69 427/390 auto. Correct carb is the #7029204. I'm currently running a remanufactured Edelbrock from summit racing (SUM-210210) until I get the $'s to locate a correct unit. The Summit rebuilt unit has 0.069 main jet; 36B primary rod and DR secondary rod. On acceleration I get a hesitation.

According to this article I found: http://www.corvettefaq.com/c3/QJetTuningPaper.doc

[Patrick H.]

Re: 69 Big Block Carburetor Decision

Hesitations such as you are talking about can be caused by the secondaries opening too quick. Get a shop manual and try adjusting the secondaries before you replace the carb.

Or, a bad accelerator pump, or ignition issues.

If you rebuild it yourself, note that most of the rebuild kits available at auto parts stores have substandard quality parts. Check out the one from Cliffs High Performance: http://www.cliffshighperformance.com/carbkits.html

[Dick W.]

Re: 69 Big Block Carburetor Decision

Uh, there is the thing about finding a "restamped" carburetor for less dollars.

[Chris L.]

Re: 69 Big Block Carburetor Decision

Thanks for sharing the info and resources. A fellow Vette owner neighbor had suggested the hesitation may be due to the accelerator pump. I may try my luck at rebuilding the carb with a good kit.

[Patrick H.]

Re: 69 Big Block Carburetor Decision

Thanks for sharing the info and resources. A fellow Vette owner neighbor had suggested the hesitation may be due to the accelerator pump. I may try my luck at rebuilding the carb with a good kit.

I'd also check the air valve as Dick suggests. If it were mine I'd buy the kit I linked to, and probably will the next time I have to get into one which will probably be soon as my 71 has been sitting for a few years. Put in the jets and rods that your engine is supposed to have (Cliffs will have them) and then go from there.

Patrick

[Brad H.]

Re: 69 Big Block Carburetor Decision

As Patrick mentioned I highly recommend Cliff's High Performance Carbs. I went thru the same issue and had my Qjet rebuilt by a local carb shop and it still had problems. I believe I heard of Cliff's on this site probably from Patrick, but I took it back off and sent it to Cliff. It took a while, but wow what a difference. I have never had a Qjet run that great. I have a near 400hp 69 350 and the Cliff's Qjet ran flawlessly on the dyno even at WOT. Normal driving is perfect all the time!
Brad Hood

[Gary K.]

Re: 69 Big Block Carburetor Decision

My 68 is equipped with a 454 with an awesome 780cfm Holley, intake is Winters cast 3963569 which I believe is from '71. The car is originally a tripower, but it's running so great with the current setup I'm really in no hurry to change until "maybe" I find the correct '68 parts.

I rebuilt the carb with standard Holley kit, used right jets for my altitude and hot weather, and standard power valve. The jets are a couple sizes smaller than what my Dad had in there at sea level. Invested three bucks in a new fuel filter, the little one right in the carb body itself, carefully adjusted the bowl floats. Before that I had flooding problems which caused a stall like you describe but now it's really dialed in.

Since you don't have the original carb, like me, it almost frees you to do whatever you want without worry about originality. The Holley 4150 4bbl on the 454 is an absolute HP torque monster, I haven't adjusted it in 8 months, although I'm not sure a Q-jet car has the same intake manifold. Good Luck!

[Chris L.]

Re: 69 Big Block Carburetor Decision

Thanks for sharing your experience and advise. Its terrific to enjoy these classic sports cars with collective knowledge.