Carburetor Recommendations Anyone???

[76sierraclassic]

My '76 is still a stock 350 with th350 tranny and the original Rochester Q-jet 4bbl carb with the automatic choke. It has almost 140,000 miles on it, and I'm having a little bit of carburetor trouble. I'm thinking a rebuild or replacement may be in order, and I'm just wondering if anyone has any suggestions. I don't want to spend a lot of money, and I don't necessarily need/want to "upgrade".

I'm fairly mechanically inclined, but I've never really worked on carburetors before. How hard would it be to rebuild it? I think the automatic choke is messed up too. How hard are they to work on/replace?

Since I've never worked on a carb before, I was also considering picking up a used q-jet to rebuild off-line. That way I would at least have a working carb in the original if I happen to screw something up. What do you guys think? If this is a good idea, how can I know what all q-jets are interchangeable with mine. The numbers on mine are 17056208 and 0866 ABT.

Any recommendations or advice will be appreciated.

Thanks,
Mike

[swervin ervin]

Any Q-jet with Chevy linkage will work just fine, without have to do any modding of for anything to hook up cable wise. Just don't get one that was computer controlled or with the dual capacity pump system. These will have wires hooked to them. I would rebuild the one you have or try to find one exactly like it or close. Check your throttle shafts for wear. This is the biggest problem with old Q-jets, but they sell rebush kits to fix this. Rebuilding a Q-jet is a snap, of course I rebuilt a ton of them in my day so I guess it's easy for me to say. The main thing is get them clean. Spray on carb cleaner won't do it. Buy some Berryman's carb dip, or similar to soak all the hard part in. No reuseable rubber parts though. It's really just a matter of watching how it comes apart and reassemble it the same way. About the only adjustments you will need to do is maybe the float height. BTW, I would replace the float too. They don't come in rebuild kits. Since you've never rebuilt one before, take plenty of notes and maybe some digital pics. Really though, it's not hard. Biggest thing is pay close attention to any linkage you have to remove. It can be confusing when you go to put it back on and can't remember how it went. The choke rod is one example of this.

Things to check:

Throttle shafts for wear.

The air horn for being warped from overtightening. Use some JB Weld on the well plugs to seal them from leaking. They were notorious for leaking gas into the intake. Some did, others didn't. Cheap insurance when you have it apart.

Check that the power piston goes up and down smoothly in the bore. These sometimes get burred a little and some fine emory cloth will slick it up.

Just some stuff to think about. It's a lot of satisfaction to rebuild a bad carb and make it work like new. Main thing is have fun with it.

[76sierraclassic]

Thanks for the info. I'll probably try a rebuild myself. I have a digital camera so I can take some pics for reference. I did that a couple of times on some guns I was working on. Lots of little springs and connections there too.

Thanks again...

Mike

[jimfulco]

If it's the carb that came with the truck from the factory, you won't have to worry about recalibrating jets & metering rods, etc. Rebuild it or get it done professionally, & be sure the throttle shaft bores get new bushings. Be sure the carb place knows you want that particular carb back, not just any old rebuilt one from another vehicle. Write down the number from the driver's side of the carb just to be sure.

[76sierraclassic]

Can anyone tell me how many cfm's my original q-jet is? I'm just curious.

Thanks,
Mike

[SanitysBane]

750 cfm, some rare ones are 800

[76sierraclassic]

Originally Posted by SanitysBane

750 cfm, some rare ones are 800

Thanks for the quick reply. I thought that might be what it was, but wasn't sure.

Mike

[76HighSierra]

Like Swervin' said, the Q-jets cannot be beat. I've used many different carbs in my lifetime with varying sucess, but lately I've been contemplating different carb types for my 454. Initially I wanted a Carter Thermoquad. I have a lot of experience with them, and when tuned right, there is not a spreadbore carb out there that will perform as well. The problem is, they are VERY finnicky and hard to get properly tuned. Plus, the resources for getting a rebuildable one that hasn't been molested by some ham-handed gearbox, are getting quite slim. I decided to try a new Holley 4175 spreadbore. It was an "OK" carb, but it did not have what I would consider to be a "very good idle quality" (I like mine to idle silky smooth), and wouldn't retain it's idle mixture settings for very long without fiddling. Not to mention, the bowl gaskets tend to "droop inwards" at the center on the top, no matter what quality the gaskets were that were used. So, I bought a used Q-jet off of e-bay to tinker with, and read Swervin's Q-jet article. Just with a few easy mods, it performed like no other Q-jet I've ever seen. It's still on my truck now, and I'm restoring (re-plating the parts, modifying/rebuilding) the original Q-jet that was on my truck. Again, using the tricks from Swervin's article, I'll be installing it after I rebuild/slightly modify ( ) my 454.

[76sierraclassic]

Originally Posted by 76HighSierra

.....and read Swervin's Q-jet article....

Where might I find Swervin's Q-Jet article? I would probably find it beneficial.

Mike

[aliencheyenne]

I am a big fan of Demon Carbs. If you can tune a Holley thery area pice of cake. Better qc control with the castings. As long as you realize that they tend to run rich and stay on the conservative side of your cfm's you will really enjoyed them.

[1972C10]

Q jets are the best on gas mileage from my exp. I have an 85 3/4 ton used to be a 454 th400 i swapped in a 355 and used the same carb with stock jetting and it got 9-13 i took it off to jet it down put a new 600 edelbrock i had on it it went to a consistent 8mpg it ran a tad better but not worth the drop in mpg I had thought about trying a vac seccy 4160 holley 600 but im not in any hurry i may try one just to fix one up and if i dont like it sell it but So far q jets have the best mileage or all of my vehicles former or present.

[apstguy]

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

[76sierraclassic]

Thanks for the links. Those articles are awesome and will be a huge help.

Mike

[76HighSierra]

Sorry for the thread hi-jack, but in relation to these articles, one of the mods is to alter your choke/secondary damper so that it fully releases in app. 1 second after vacuum is lost. I had installed a brand new one on my Q-jet, just a few months before I removed the carb for restoration. The article says to enlarge the orifice on the vacuum nipple of the damper to decrease the time it takes to release. I performed this mod with progressively larger small drill bits. It was to no avail. If it made any difference, it was minimal and almost imperceptable. Is there a "performance" oriented damper available anywheres? Again, sorry for the hi-jack.

[swervin ervin]

Marc,

the orifice you need to drill out bigger is down inside the tube. It's not the tube hole itself. It has to be a straight tube unless you have a curved drill bit.

Seriously, the orifice is right where the tube meets the canister.

[76HighSierra]

Originally Posted by swervin ervin

Marc,

the orifice you need to drill out bigger is down inside the tube. It's not the tube hole itself. It has to be a straight tube unless you have a curved drill bit.

Seriously, the orifice is right where the tube meets the canister.

Ahhh, that explains it. Thanks, Swerv!!! I really didn't want to junk a brand new damper. The reason I assumed it was the hole on the tip of the vacuum nipple, was the fact that the article wasn't very clear on that and didn't say the restriction was at the bottom of the nipple, and that the hole in the end of the nipple was very small. Even smaller than 1/16th. Just wanted to holler a thanks to you, Mike, for the awesome articles. All the Thermoquads I've tweaked for spreadbore performance, and all of the time I've spent on them could have been much better (and not to mention 1/4th of the time ) spent on a Q-jet. I'd still like to get a good buildable thermoquad to build up for performance usage, as a comparrison to the tweaked Q-Jet. If only the thermoquads weren't so finniky. Many people hate them, but I absolutely love them. I just don't have the time to devote to tuning one of them repeatedly anymore. Q-jet, baby, yeah!! By the way, the nipple on my damper is straight.