Blew the 400 up

[OutlawDrifter]

Are the secondary butterflies froze up?

Good choice on the carb, a properly built and cared for QJet is as close to fuel injection as you can get with a controlled fuel drip. I'll +1 for Cliff Ruggles' book if you don't have it already, well worth the money. His company is where I used to buy all my rebuild parts from.

 

[Deadman walking]

If you're dead set on running that thing.. and you probably already know this.. check all the mating surfaces to be sure nothing is warped, and check the condition of the threads at the inlet/fuel filter nut. Back in the day (and I mean 30+ years ago) I recall having to dig through a mountain of Quadrajet carbs just to find enough pieces to assemble one that was going to work. Warped air horns, warped throttle plate, and of course the always-troublesome stripped threads for the fuel filter nut. I've seen more than one just turn into powder there. I've also seen a gorgeous '68 GTO burnt badly due to the owner's insistence on using a "repair" kit on his because he wanted to keep the original numbers-matching carb, which I understand, but it would have been better kept in a box on his garage shelf instead of continuing to leak on his engine.

Richar

Buick was the first of the five divisions to mass-market the "800 cfm" primary size.

Pontiac had some "special" Q-jets on the top-dog engines; and all the other divisions eventually used the "800" on at least some engines after Buick started the trend.

I can't tell if the carb pictured is the "750" version or the "800".

For the record...Cliff Ruggles book on the Q-Jet is spectacular. But the publishing company is a bunch of dirtbags that print the thing in Communist China while charging Made-In-USA prices for it. They also limit the page count to 144 even though most of their books really need more pages to do the subject justice.
www.cliffshighperformance.com/

Cliffs High Performance Quadrajets – Quadrajet Rebuild Kits, Cabruretor Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning

www.cliffshighperformance.com/product/how-to-rebuild-and-modify-rochester-quadrajet-carburetors

How to Rebuild & Modify Quadrajet Carburetors – Cliffs High Performance Quadrajets

Buick was the first of the five divisions to mass-market the "800 cfm" primary size.

Pontiac had some "special" Q-jets on the top-dog engines; and all the other divisions eventually used the "800" on at least some engines after Buick started the trend.

I can't tell if the carb pictured is the "750" version or the "800".

For the record...Cliff Ruggles book on the Q-Jet is spectacular. But the publishing company is a bunch of dirtbags that print the thing in Communist China while charging Made-In-USA prices for it. They also limit the page count to 144 even though most of their books really need more pages to do the subject justice.
www.cliffshighperformance.com/

Cliffs High Performance Quadrajets – Quadrajet Rebuild Kits, Cabruretor Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning

www.cliffshighperformance.com/product/how-to-rebuild-and-modify-rochester-quadrajet-carburetors

How to Rebuild & Modify Quadrajet Carburetors – Cliffs High Performance Quadrajets

ive used that book before actually I copy somewhere. I got a 1979 q jet from a Pontiac 301 to work on a 73 Camaro 350 smog motor by using that book. But this carb is a 71 Buick 455 carb. And it's an 800.

 

[Deadman walking]

Are the secondary butterflies froze up?

Good choice on the carb, a properly built and cared for QJet is as close to fuel injection as you can get with a controlled fuel drip. I'll +1 for Cliff Ruggles' book if you don't have it already, well worth the money. His company is where I used to buy all my rebuild parts from.

Yeah the secondaries are it looks like it's been sitting outside for a while. And thanks I figured 800 was better than what does TBI flow? Like 435 or something?

 

[Deadman walking]

Whoops sorry here's some better pictures

 

[PlayingWithTBI]

what does TBI flow? Like 435 or something?

My bored to 46mm (from 42) flows 650 CFM which is plenty to support a 5.7L up to 6,000 RPM

 

[L31MaxExpress]

I recommeend the newest Q-Jet you can find that does not use a mixture control solenoid. Those are Mod Quads, about 1975+. The larger venturi version flows up to 850 cfm. The 1980-1984 Chevy Truck Q-Jet casting is the same one that Edelbrock used for their Performer RPM Q-Jet. Cliff goes into detail on this in his book.

 

[95burban]

Yes I do have a legitimate reason to run a q jet.

Once the wiring gets too old on the TBI harness you start chasing down what I call "phantom problems". So let's say you think a maf sensor going out and you replace it and it acts the same with stumbling.

Well broke wire,bare spots arching out etc. I keep chasing these same exact problems with the TBI. So I clip the purple wire with the white stripe as a trigger wire and then the red ignition wire adjustable fuel pressure reg, and an hei distributor. More air flow than the TBI plus I can tune out the q jet to get better mpg than a TBI. No more sensor computer or bs. I'd take that deal all day long

I totally understand. I’m not a huge fan of q-jets, I’m more of a mechanical secondary 4150 type of guy.

 

[L31MaxExpress]

Yes I do have a legitimate reason to run a q jet.

Once the wiring gets too old on the TBI harness you start chasing down what I call "phantom problems". So let's say you think a maf sensor going out and you replace it and it acts the same with stumbling.

Well broke wire,bare spots arching out etc. I keep chasing these same exact problems with the TBI. So I clip the purple wire with the white stripe as a trigger wire and then the red ignition wire adjustable fuel pressure reg, and an hei distributor. More air flow than the TBI plus I can tune out the q jet to get better mpg than a TBI. No more sensor computer or bs. I'd take that deal all day long

For the record, a carb will not get better mileage than a TBI unit. You can dial in the carb however you want to and I am still going to beat you in MPG with TBI while having better manners.

As for your phantom harness issue, maybe if you leave the harness exposed and it degrades. Keep it loomed and it works for years. Even if a harness became an issue, several companies make 100% NEW TBI harnesses. A harness is cheaper than a carb conversion. Sensors are also very simple and reliable. TBI only has 5 sensors. MAP, TPS, CTS, Ignition Control Module, and a Knock Sensor. Not exactly rocket science.

 

[Deadman walking]

My bored to 46mm (from 42) flows 650 CFM which is plenty to support a 5.7L up to 6,000 RPM

I just think it would cost more to build a TBI than a carb. Plus I like the idea of 4 jets.

 

[Deadman walking]

I totally understand. I’m not a huge fan of q-jets, I’m more of a mechanical secondary 4150 type of guy.

Oh yeah not a lot of people like them are I've heard people say they leak,and shoot gas and oil. If you get a good rebuild kit and replace those lead well plugs with brass and seal them with jb weld that solves most of the problems right there.

Seals or bad springs bent rods or my case they simply left the damn thing outside and it's seized. They can support up to about 650 hp but I'm not going that far this is just a daily driver I just want 1 HP per cubic inch. If it's rebuilt good it's actually not a bad carb

I'm just running it for good balance of economy and power with vortec block I'd say about 310 for now. I do have a 750 ultra double pumper but it's got mech secondaries not really all that great for a truck.

Plus I like the smaller primaries and larger secondaries if I decide I'm bored and bury my foot.