I have a totally stock 69 GTO convertible w/ manual trans. I've rebuilt the motor years ago and also, rebuilt the stock carb. The motor ran fine, but the carb started loading up and eventually started running rich. The carb has been getting progressively worse and since the motor is still fresh (low miles), I won't run the motor with that carb for the fear of damage.
I read a book on Rochester carbs and took apart the carb. I checked everything from floats to tolerances to expoxing up plugs. Still, when I installed the carb and started it up...still loaded up. I also checked the timing, dwell, compression, stock choke and vacuum...everything is right. So the carb is singled out.
Now the carb is the correct year for the car, but it's a Rochester made by Carter AND no serial numbers on housing. I don't know if this was deliberately done by the factory or?
Well, to make my little story short, I want to get my GTO running again. Just for the sake of getting it running efficient, what aftermarket carb. would be the best replacement for a stocker? I was looking at Demon Road, 625 cfm. Good? or no?
Thanx for reading and replying

Go check on a price of a 600 cfm Edelbrock and Edelbrocks are the best street carbs.The Edelbrock is the easiest to set up out of the boxAvoid a Holley,a huge piece of junk and they are only good for racing applications only.I hear a lot of horror stories about Holley carbs used as a street application.Had a Holley on a 1966 Nova with a stock 327 and it ran like crap and stalled a lot.The Demon carb is a good carb and is very expensive

First off, rebuilding the Q-Jet isn't "rocket science", but it IS a little difficult. We ALWAYS replace the fibre float with a brass unit. When I did carbs in a dealership (Pontiac, Buick), every time we "openned" one, it got a new float. Now, Borg Warner, NAPA, etc. provide brass floats for most applications. The "heavy float" is where the nickname "Quadra-Flood" came from. The other area of concern is the throttle shaft where the cable hooks up. They're known to wear in the baseplate. Bushing it cures that.

Carter was sitting "idle" (Chrysler products weren't selling as well as GM at the time), and Rochester was BURIED, so they "farmed" manufacture of many Q-Jets to Carter. I don't believe original GTO carbs were Carter except the SOME of the '67s. That's not an "absolute", as records are a bit "sketchy". More than likely, the carb had been replaced somewhere in a "past life". If a 350-horse 400 with manual trans, the carb number should be 7029263 or 7029267.

The Edelbrock carbs are fine on mild 350 Chevys. They DO NOT WORK on a 400 Pontiac. Oh, it will run and get down the road, but it will never have a good transistion between primary and secondary, or a crisp, smooth idle. And a 600 CFM carb is WAY too small for a 400 CID engine. The E-carbs are a cheap "knock-off" of the old Carter AFB (some AVS as well). GM abandoned AFB in early '67 in favor of Q-Jet. MUCH better carb.

Holleys are fine for racing and high-powered street cars. Actually, none better. BUT... For a relatively stock 400 Pontiac, Q-Jet is the only logical choice. Contact Cliff's High Performance in Mt. Vernon, Ohio, for the best book and parts for a Q-Jet available anywhere. He has NHRA C/SSA Firebirds running on the index in the low 9s, with Q-Jet. Q-Jet may very well be the best production carburetor ever made by anyone (IMO).

Jim

Don't forget the troublesome leaking main well plugs that used to torture me on Cadillacs I repaired back in the day. LOL

MW,

Right you are! That is well-covered in Cliff's book. Actually, if you're a Q-jet "fan", I would recommend the book, even if you aren't planning a carb build in the near future. His techniques and knowledge will BLOW YOUR MIND! Not a bad guy, either. Of course, he IS a Pontiac racer! (:-

Jim

Edelbrocks do run good on Oldsmobile and Pontiac engine swith the performance series carbs.I know an used car dealer that had a 1949 Plymouth street rod with an Oldsmobile drivetrain,had an Edelbrock which my father had to rebuild and it ran good after the rebuild just before sending down the auction block

thanks guys for replying, it's very informative.
MrPBody, I've also been thinking about the throttle shaft or bushing being worn. I know that has to be taken care of by a professional, replacing a throttle bushing is not for backyard mechanic (possibility of wrecking the carb housing). I'll have to look into that.
I guess the only way to go is sticking with what the factory put in the car. I know all my friends would agree. Probably have to sit down and go through everything from metering rods and jets to float and throttle shaft. See where the culprit lies.
Yeah, I agree, Holleys are not good street carbs. I had a 69 Nova with a healthy 350 and ran a Holley 650 dp on it. I can't tell you how much problems I had with it, even when I read books and tried to become an authority on the carb. So, I ran a reliable 600 Edelbrock for the street and bolted the 650 Holley on for the strip. I had fun with the Holley though on the strip and trying different set ups with it, doing it right at the track...what's racing is all about.

Fred,

I suess we have different definitions of "run good"... A Pontiac or Olds V8, unless smaller than 375 CID, will not live up to its "potential" with any carb smaller than 750 CFM. the 400 Pontiac "likes" an 800 CFM carb to really perform well. The 730 CFM Q-Jet ('69) is okay until about 5,400 RPM, where it will promptly "fall on its face". In a stocker, this is okay, as 5,200 is the recommended "redline".

I believe one of the differences is the level of "expectations". Since we build high performance Pontiac and Olds V8s here, we "expect" more out of them than the average hobbyist. We're not "happy" when they can ALMOST beat a Chevy or a Mope. We're happy when they BEAT them! We've been MUCH happier the last couple of years...(:-

We use AED Holleys almost exclusively, on our street "strokers" (600 HP 461 Pontiac). Zero issues in 8 years. A carb is only as "good" as the "last man in".

Jim

Yeah, I agree, Holleys are not good street carbs. I had a 69 Nova with a healthy 350 and ran a Holley 650 dp on it. I can't tell you how much problems I had with it, even when I read books and tried to become an authority on the carb.

FWIW, don't blame Holley. IMO you were using the wrong one for the application. (I made the same mistake.):)
There are many different kinds of Holley carbs. IMO it's a common mistake to use a double pumper and expect good street performance.
This is why Holley makes a vacuum secondary carb in almost all their configurations. The vs carbs are much better for street use than a db... yet still work well on the track.

I will say that every Holley carb I have ever used needs some tweaking to get them set up right, even when you match the application to the exact carb that Holley recommends.

Inevitably, the Holley carb is jetted too rich for milder engines. Often, one needs to play with the accelerator pump, power valve and vs spring, along with the jetting to get optimal performance and economy. Once that's done, Holleys are fine on the street, even though IMO they use less accurate fuel metering methods than other carbs, especially related to the 'power valve'.

At present, I have a 650 Holley dp on my '69 GTO, a 750 vs Holley on my Olds 455, a stock Autolite 4bbl on my Ford 429 and 460, Holley 390 vs om my 2.8, and Quadrajets on my small block Chevies.
Surprisingly, the Autolite provides the smoothest, flawless all-around performance, with the 750 vs providing the most power.

By comparison, the 650 dp does not work particularly well on my GTO, imo because it is the wrong carb for the job.

MR,

Sorry for the duplicate post. I have no idea... (:-

Agreed, getting the RIGHT carb is the main thing. That GTO (I didn't know you had a REAL one...) is CRYIN' for a good Q-Jet!

Jim

Agreed, getting the RIGHT carb is the main thing. That GTO (I didn't know you had a REAL one...) is CRYIN' for a good Q-Jet!

Some of my GTO trouble is also due to the intake.

I bought my GTO years ago, with an old Offenhauser "Dual Port" intake and the Holley already on it. The previous owner was a buddy of mine and did not understand intake principles... so he thought this combo was a good idea.

The Dual Port intake is a very interesting attempt to match runner diameter with airflow... somewhat similar in theory to variable-length intake runners found in some 4-valve heads. But if it worked well, they would still be made.

I also have an Edelbrock alum. dual plane manifold, and boxes of Holley and Q-Jet carbs. At some point I'll put together a better combo for the car. It may not be original Poncho but will work better than the present combo.

Agreed on the Offy DP. Good idea, poor execution. I HAVE seen one 400 combo with it that workled pretty well, though. He used it, an AFB (625) and the old Comp 268H cam, "advanced" 4 degrees. The thing made so much low-end, it would tear the tires right off. It fell flat on it's "face" at 4,500, but got there "in a hurry". With 3.08 gears, the car was actually pretty quick through a 1/4 mile!

Jim

That's excellent input. I'll keep it in mind :)