Grant1424

Hello everyone, I need to replace my original carb. on a 1972 Conv. Cutlass. It has the original rocket 350 engine and intake. I've tried to have it rebuilt but all 4 barrels still will not open so I am going to replace it. I wanted to know which carb works best with the Oldsmobiles. I want something that will bolt directly on the stock intake and that is easy to work with. I am more concerned with performance than gas mileage.

If you all could post links and or prices with the model of the carb you suggest that would be very helpful. That way I'll know where to purchase it.

Thanks in advance!

olds 307 and 403

Street Demon 625 cfm. Very similar to Qjet in design and will bolt to your stock intake. There are tuning parts available plus polymer and aluminum body options.

Grant1424

Thank you for that info. It looks like Summit has them for $329.
http://m.summitracing.com/parts/dem-1900

hookem horns

Couple of easy things to try first, maybe you already have done them. May seem obvious, but does the throttle cable allow the carb to fully open when the gas pedal is floored? There's also an adjustment screw for the secondary spring tension on choke side of the carb. Have to loosen the hex set screw below it first and does not take much to make them open sooner (careful or it bogs) or later. Who did the rebuild and have you talked to them?

joe_padavano

What does that mean, exactly? You can't see the secondary throttle blades with the carb mounted on the intake, and on a Qjet the secondary throttle blades are mechanically actuated and ALWAYS open when you press the throttle unless the throttle cable is damaged or not moving fully.

I'm guessing you are looking at the secondary air valves on the top of the carb. These will NOT open fully if you are simply revving the engine in park. THIS IS NORMAL, which is why you haven't been able to "fix" it. A far better (and cheaper) way to go is to understand how the Qjet works and adjust it properly. You won't find a better carb for a stock or mildly-built street-driven Olds, especially the original Qjet that is calibrated for your engine.

Grant1424

I'm not mechanic so I've taken the car to two different shops, the first shop stated I needed a new carb and stated for the price and headache I would be better off replacing the original. I wanted to keep my original carb so I took it to a second shop who works on similar classic cars but they basically told me the same thing. They worked with a guy who attempted to rebuild it but had a hard time finding parts. They cleaned up real well and replaced all the vacuum hoses, the car runs much better but it's still hard to start sometimes and the secondaries may have opened once ( which was the 1st time they have opened since I've owned the car ). At this point I'm going to replace the carburetor.

From what I have read so far on the Internet, Summit, & YouTube ( Chuck's Garage ) about the Demon carburetors they seem to be the best way to go for me. Thanks again to olds 307 and 403!! for steering me in the right direction.

1970-W30

You need to find someone who knows Qjets. Replacing a Qjet with another brand just because it appears that the secondaries don't open, is just pissing away $300+ dollars ...........

joe_padavano

OK, both shops are either stupid or blowing smoke up your butt. Qjet parts are extremely easy to get. The bottom line is that there is FAR more profit for them to bolt on a new carb than to make the one you have work correctly.

More to the point, you keep saying that the secondaries don't open. HOW do you know this?

Grant1424

And when I try to open the secondaries I'm always driving the car, not revving the car in park.

joe_padavano

And again, unless you are Superman and have xray vision, how do you know the secondaries are not opening?

whiskey runner

i agree with the others .. the original carb is best for your car and wallet.. anyone with a little experience should be able to rebuild your carb and even tune it to meet your specific engine needs unless it is severly damaged somehow, but that should be obvious

Grant1424

I've tried flooring the accelerator , while driving many times and the car just gradually pick sup spread... I've floored it on one occasion and the car responded really different , with extra power, sound, and it felt different. The mechanic advised me that was all 4 barrels opening up. If I'm understanding you correctly, you're telling me that no one can tell when the secondaries open unless they're superman with X-ray vision?

Grant1424

Here is the video of the Demon carburetor from Chuck's Garage where he can tell when the secondaries open. And this is what I'm referring to.

drop top olds

Dean Oliver will make that Q-jet sing for you.

http://deanoscarbs.com/

Save the Q jets!

Grant1424

Hey, THANKS Drop Top Olds!!!! That's what I'm talking about! That's the information I needed!!! I am definitely going to send the Q Jet to Dean. That solves everything.. I really do appreciate that information.

Grant1424

I am originally from Little Rock, AR... Wow what a coincidence. I've been to Stuttgart, AR. many, many, many times... What a small world. Thanks everyone for your suggestions and input l.

455man

Basically Joe is saying you'll almost never see a quadrajet open the secondaries. The bottom throttle blades will open but it takes about 3-5 seconds floored for the top air valves to open up. And you dont wanna do that in park. It could be just out of adjustment.

joe_padavano

What I'm telling you is that lack of acceleration can be caused by a lot of things, including an intermittent kickdown operation.

Again, on your Qjet the secondaries are mechanically actuated and ALWAYS open. (Yes, I am aware that some versions of the Qjet do lock out the secondary throttle plates with the choke. The 1972 Olds carb in this thread is NOT one of those - it uses the air valve lockout I describe below)

The air valve on top of the secondaries has a lockout that is connected to the choke. An improperly adjusted choke or a sticking choke linkage can cause this to work sometimes and not other times, which is another possible explanation for your problem. A good mechanic who understands Qjets would know that. Most "mechanics" don't have the skill or patience to properly tune a Qjet and thus just tell their customers to spend hundreds of dollars to replace them (again, improving profit margin). And keep in mind that even a good Qjet specialist won't be able to properly adjust the choke on your particular car without having the car in front of him. This final dialing-in needs to be done on the vehicle.

Grant1424

Thanks Joe

NHolds

I have had a Quadrajet, an Edelbrock, and a Holley on my Olds engines. The one with the best 'feel' is the quadrajet. I just took my quadrajet off because of starting issues... the bowl would run dry after a couple days, and it would need some help starting. Put the Edelbrock carb on in the meantime. The Edelbrock has a much nicer idle, and much better off the line acceleration, but doesn't have a great 'feel' when you put it to the floor. It goes.. but not the same as a quadrajet. And, the Edelbrock is new, vs 42 year old Quad

I haven't had a Holley for quite awhile, but I remember it was along the sames lines as the Edelbrock.

Grant1424

Thanks NHolds!! Very nice car in the signature!!!

cutlassefi

Just curious, did you ever bother rejetting the Holley or Edelbrock?

NHolds

The Holley was on a 455 with Edelbrock Performer manifold, and yes, played around with it quite a lot. Very nice carb, but never had the same feel as a quad. The Edelbrock is right out of the box. Only thing I have done to it so far is change the position of the accel pump rod.. wasn't getting enough fuel. I don't drive the car all that often so I don't know if I will play with the Edelbrock yet.

hookem horns

X2 on what Joe said about checking the kickdown. I may be over simplifiying it a bit, but 2 things should happen if you floor it from a steady cruising speed (say 40-50mph). First the transmission downshifts which should be immediate and noticeable as the rpm's increase. This is called a "passing gear" by many but is just a downshift triggered by a cable (TH350, likely in your 350/4bbl car) or switch (TH400 or older Jetaway). After that, the secondary air valves on the carb will start to open. While you cannot see it, a quadrajet make a pretty distinctive (and nice) howl as this happens and is more noticeable with an open element air cleaner. Hope we are helping you understand your car before opening up the wallet.

joe_padavano

Correct, but if the trans doesn't downshift, the engine RPMs won't climb nearly as quickly, which means that despite having your foot to the floor, there isn't enough airflow to open the air valves (the secondary throttle blades WILL be fully open). That means you won't hear any "howl", either. This is not an indication that the secondaries are not opening, just that the engine RPM isn't high enough to need them.

firefrost gold

I got a Carb from SMI carbs was butiful to look at I dropped it on hooked it up and was very sad with the way it ran Between a few people on Performance years a pontiac site they got me very close. My secondary was way off and I had to tighten it up slow down the opening up then played with the other settings and it work good when I was done My 750 edelbrock
was about the same after i played with it also I as I think your shop might like working on the edelbrock so thats why they want you to change it out JMO Good Luck

NHolds

Here is a bottom view of wide open throttle... all 4 open
IMG_20140327_165034205_zpsfhwvjb70.jpg

Here is the view from the top at wide open throttle... (carb is off the car).
IMG_20140327_165221751_zpslqbzd8yi.jpg

NHolds

Here is the linkage that manually opens the secondaries....

IMG_20140327_165122525_zpsihr2axf7.jpg

joe_padavano

But again, you won't ever see this just by revving the throttle in park. The question frequently comes up about this.

NHolds

Yep... that's why I mentioned it's off the car....

Now, if the butterflies aren't opening.. that's just an adjustment. You need to open your primary butterflies all the way to see if the secondary butterflies are released. There is a little pc that locks the secondary butterflies until they are wide open... you can kinda see it in the second pic.

Grant1424

Another thing about my Q Jet carb, I couldn't get them to open with my hand like the above picture, neither could the mechanic that I took it to, to have it rebuilt. Maybe the pc was locked , I'm not sure but the primaries would open all the way and close with ease... The mechanic told me that was my problem ... But who knows, I've contacted Deno and he quoted me a price of $300 + shipping which is perfectly fine with me. I'll sending it off to him and that way I'll know it'll be done correctly and I'll be able to keep the original.

hookem horns

We want to help but still not convinced you have carb issues yet. Holding the primary butterfly wide open should release the lockout on the secondary air valves, allowing you to push them open (the springs will offer slight resistance) Move on to another mechanic if he did not do this but said your carb was broken.

Are you certain you are getting WOT when the pedal is floored? Have someone floor it (not running, of course) and see if the linkage on the carb still has more travel.

Also not sure the car is downshifting when you punch it, which would help create the rpm's/airflow needed to make the secondaries open. As Joe has said many times, a QJet needs airflow (rpms under load) to open the seconday air valves, which happens progessively based on demand. From a steady cruise, manually downshift and then floor it to see if that gives the kind of response you said it did once.

Last but not least, is the engine properly tuned, especially the timing? Carbs are often blamed for ignition issues.

drop top olds

As others stated be sure to check out the throttle cable and the trans cable. I sent a "core" 7041250 to Dean. He took the time to set it up based on information I provided about the engine/trans etc. When I got it back from Dean it was dead on. The Q-jet has been on my car for over nine years. Only thing I have had to do is change the fuel filter have not touched it otherwise. Dean will return to you a carb that will not have any issues. I highly recommend Dean Oliver for any Q-jet work.