Difference b/t DR and DA secondary rods?

[EricS76]

I've been looking at remanufactured Q-jets. I found one at a good price, but it's got DA secondary rods. From what I've read, the DR rods are the best, but what's the difference between the DR's and DA's?

Here's the carb setup i'm looking at:
73 jets
52M primaries
DA secondaries

Is that a good combo? The engine is a stock 350 with headers, no egr.

[EricS76]

DA rods are slightly richer than DR. This is what the carb rebuilder told me for FYI.

I opened up my origional carb and cleaned it out good. Put it back together and it works good now. It already had DR rods in it, but an "I" hanger. My vaccuum canister is still taking about 3 seconds to open even after I drilled it out. Can I pick a new one of these up at the local auto parts store?

[swervin ervin]

DA rods are too rich for a stock 350. Heck, they are too rich for a modified 350. DR rods are the only way to go, IMO.

DA rods at the taper from start to tip:
.1333, .1244, .1075, .0847, .0577, .0440, .0440, .0440

DR rods at the taper from start to tip:
.1323, .1250, .1093, .0882, .0746, .0581, .0570, .0570

As you can see, the DA rods have a longer and much smaller diameter power tip. This is fine for a lot of WOT driving, where your engine will need lot's of gas. On the street, this will be a tuning nightmare. If you had a big block, these rods may be needed. But a small block, even one with a bigger cam and other stuff to make use of more gas, it's way overkill.

As for the 52 primaries, a lot depends on what size jets you have. I'm running DR rods in the secondaries. On the primary side I'm running 48 rods and 73 jets. I've read a lot of stuff about where you need a difference of .030 between the rods and jets. I never could get my setup to work with this much. I found it ran best cruising and part throttle with a difference of .025". Now after saying this, you can't stick in some big arse jets and expect to make it work with some big rods to get it back to the right difference.

Do you know if the Q-jet you are buying has the APT adjustment? Older Q-jets didn't have a APT and required different settings on the primary side. The APT screw will hold the rods out of the jets at high vacuum situations and lets you use smaller jets and rods. Without the APT, the rods will be pulled down into the jets farther thus requiring larger jets to get the same effect.

Read these articles.

http://www.73-87.com/7387garage/drivetrain/damon.htm

http://www.73-87.com/7387garage/drivetrain/damon2.htm

http://www.73-87.com/7387garage/drivetrain/myqjet.htm

http://www.73-87.com/7387garage/drivetrain/qjetidle.htm

On another note, be real careful where you buy a remanufactured Q-jet from. Most so called carb rebuilders don't have a single clue what they are doing when it comes to rebuilding a Q-jet. Buying one from a company like this is a good way to waste some good money in a big hurry.

[EricS76]

Well as it turns out, I got mine working right with a little cleaning. I read most of those articles the other day, and that's where I learned 99% of this info about Qjets. Very good articles. I've got a couple of questions though. I tried to set the A/V spring to 1/8-1/4 past zero, but it wouldn't close itself until I got the screw to about over 1/2-3/4 turns. Is it supposed to be set that loose, or is my A/V shaft binding or something? Also, my vaccuum cannister shaft for the A/V takes about 3 seconds, even after I drilled the port out a little. Is this a part that most part stores will have or not?

[swervin ervin]

To set the spring you need to make sure the spring hook is just meeting the little rod on the shaft when the valves are held closed with your fingers. This is exactly zero tension. Now when the carb is held upright, the least amount of tension should close the valves or at least start to move them a fair amount. I've got mine set at 1/8 or so and it works perfectly. Besides this, with the choke pulloff/AV damper hooked up, you could just about not even have the spring at all. The damper will hold the valves closed anyway. If your spring adjustment isn't working right, the shaft could be worn and maybe binding a tad. It's also possible the secondary rod lifting cam might be worn or rubbing in a wrong way causing drag.

For the canisters, does your carb have a rear (secondary) only or front (primary) only? If it's a rear damper, you can't adjust these, or at least I haven't found a good way. You will need to convert to a front damper. I haven't tried to convert to a front unit from a rear but it's possible. You will probably need all the linkage to make it work. I would try and find a donor at a junkyard for this and change what's needed to make it work.

You can buy new pulloffs at http://www.carburetion.com/quadrajet.asp

Mike

[EricS76]

Yeah i think I have some binding. I'll try to get it cleaned up somemore and reset the spring tension.

My carb only has the front damper.

Thanks for all the info.