Carb choice for 350

[75K15]

This site is freakin awesome! whoever came up with the idea of putting all these BA's and their Chevy's up on one site is a genius!

It's unfortunate that I didn't find this site until now... I'm hoping someone can help me with my problem... I have a lifted '75 k15 I bought a couple months ago. I've done alot of maintenance bs (filters, plugs, etc) so far but now it's time to get to the meat and potatoes. I want to ditch my old quadrajet for something a little more reliable.. I heard the quad is responsible for my looonngg starts. I did some quick research and found that Holley makes a carb called the "truck avenger" : 670 square bore for about $400. Benefit being the tilt fuel control for when out 4x4'in... sounds good but does a univ square bore fit my application. Stock is spread bore I think. Also Holley makes a 650 bolt on replacement for the quadrajet($350), but Summit says it only fits the '69 k15. I am an engineer so I pick things up real quick, but this is the first project I have started outside of my bike (72 honda 350) Is it gonna be tough for me to install something like the "avenger" by myself? I have a buddy with a 73 c10 that would probly help if I got a half rack, but I would rather do it on my own.

I'm open to suggestions... Ideas? Type, price, supply?

Thanks guys!

[Srubydo1986]

650 cfm

[gchemist]

Welcome to the site.
Edelbrocks 1406 is my choice. No more than 650 CFM for a SB. The carb is easy to tune. All you need is a vacuum guage. http://www.centuryperformance.com/vacuum.asp

[Pyrotechnic]

For a stock headed and cammed 350, there is actually no better carb than a properly functioning Q-Jet. My Q-Jet starts up on the first crank everytime, and the gas mileage and power are great. Even letting the truck sit for a week, it only takes a few extra seconds for it to start up.

The Q-Jet on my truck is a holly remanufactured unit. It sounds like yours is long worn out. However if you have done modifications to the motor, it's usually cheaper in the end to go with Edelbrock or Holley.

[75K15]

Originally Posted by Pyrotechnic

For a stock headed and cammed 350, there is actually no better carb than a properly functioning Q-Jet. My Q-Jet starts up on the first crank everytime, and the gas mileage and power are great. Even letting the truck sit for a week, it only takes a few extra seconds for it to start up.

The Q-Jet on my truck is a holly remanufactured unit. It sounds like yours is long worn out. However if you have done modifications to the motor, it's usually cheaper in the end to go with Edelbrock or Holley.

I'll keep that in mind before I scrap it for something else. Maybe a rebuild kit?

[stepside454]

Originally Posted by Pyrotechnic

For a stock headed and cammed 350, there is actually no better carb than a properly functioning Q-Jet. My Q-Jet starts up on the first crank everytime, and the gas mileage and power are great. Even letting the truck sit for a week, it only takes a few extra seconds for it to start up.

The Q-Jet on my truck is a holly remanufactured unit. It sounds like yours is long worn out. However if you have done modifications to the motor, it's usually cheaper in the end to go with Edelbrock or Holley.

I totally agree, possibly consider a Stage1 version from Jet performance, can get them through Summit. Also try Val Hedworth in Macon Missouri, hes a long time Q-jet wizard & NHRA Stock Eliminator champion. He knows q-jets very well.

[Grande Rojo]

Bolt on a Holley 670 Street Advenger. Yes, they make a adapter for Square Bore to Spead Bore

[Pyrotechnic]

http://store.summitracing.com/partde...5&autoview=sku

Never had any experience with the Summit reman carbs but that looks like a good deal for the stock divorced choke setup if yours is working good.

http://store.summitracing.com/partde...5&autoview=sku

Theres also that one if you want an electric choke instead.

[mexgrhd68]

Originally Posted by Pyrotechnic

For a stock headed and cammed 350, there is actually no better carb than a properly functioning Q-Jet. My Q-Jet starts up on the first crank everytime, and the gas mileage and power are great. Even letting the truck sit for a week, it only takes a few extra seconds for it to start up.

The Q-Jet on my truck is a holly remanufactured unit. It sounds like yours is long worn out. However if you have done modifications to the motor, it's usually cheaper in the end to go with Edelbrock or Holley.

Is that the trick to some great gas mileage, parking your truck for a week? I knew I was doing something wrong.

[Pyrotechnic]

It's either that or a Prius.... The 14 or 15 MPG i've been getting is pretty damn good though.

[1983shorty]

buy this guys book and rebuild it yourself . he built the quadrajet for my gto.
i am not a carb guy so i had him build it for me. his book is supposed to be awesome. he has a 6 month waiting list to build a carb. really nice guy too. i well built quadra jet will give better fuel mileage than a holly. i have a holly 650 on my truck. it SUCKS as far as i am concerned.

http://www.cliffshighperformance.com/

[piecesparts]

Originally Posted by 75K15

I'll keep that in mind before I scrap it for something else. Maybe a rebuild kit?

Make sure that it is a Rochester Q-Jet not a Carter Q-jet. The quality of the carb body is better in the Rochester unit, than the carter.
The Carter does not have the brass inserts for the secondaries to fit through and they tend to channel out and cause a slobbering effect, when you transition from the primary needles to the secondaries.

[75K15]

Originally Posted by piecesparts

Make sure that it is a Rochester Q-Jet not a Carter Q-jet. The quality of the carb body is better in the Rochester unit, than the carter.
The Carter does not have the brass inserts for the secondaries to fit through and they tend to channel out and cause a slobbering effect, when you transition from the primary needles to the secondaries.

Yeah, its a Rochester.

[streetstar]

Originally Posted by Grande Rojo

Bolt on a Holley 670 Street Advenger. Yes, they make a adapter for Square Bore to Spead Bore

Don't use an adapter on a 4x4 applcation if you can help it-- you need all the torque you can get, and a thick aluminum spacer takes torque away.

Edelbrock, (and many others) make appropriate manifolds for the carb styles

[streetstar]

[QUOTE=gchemist;2359185]Welcome to the site.
Edelbrocks 1406 is my choice. No more than 650 CFM for a SB. http://www.centuryperformance.com/vacuum.asp[/url]

Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .

A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .

GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog

[piecesparts]

[QUOTE=streetstar;2361267]

Originally Posted by gchemist

Welcome to the site.
Edelbrocks 1406 is my choice. No more than 650 CFM for a SB. http://www.centuryperformance.com/vacuum.asp[/url]

Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .

A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .

GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog

You are absolutely right in your assmptions that an engine has to be fed according to the demand. However for everyday street driven vehicles, the overcarburetion of a 750 will (and believe me, I have seen it) cause a slobbering problem at the stoplights. Your top end will be EXCELLENT but your daily drivving will be poor. The Q-Jet has small primaries and then transition to the secondaries which gives the 750 effect on them. Where a Holley, Edelbrock or Carter square bore four barrel has a slightly larger primary when it is a 750 and that is detrimental to daily driving.

This all depends on a couple of other factors 1) weight of the vehicle--a truck is heavier than a Camaro, so it will respond more sluggishly, unless really geared low. 2) the gear ing is the next thing---people of today are trying to get the gearing high enough to keep the RPMs down, that does not work well with a larger bore carb. 3) The 750 will plate out residue on the intake valves as it works in daily driving and cause more sluggish response as time goes on (seen the effects in a machine shop atmosphere.

Holley and Edelbrock corporations; both will tell you to stay at or below a 650 CFM on a 350 motor and even a 383, if it is street driven; to keep the air flow up and the efficiency of the carb working for you, that way the high velocity will make up for the heavier vehicle weight. Granted, my 383 ran hard all the way up to 6000 RPM with the 750, but I could not get the thing to work right on the street--I had to make a decision, so I did not go to the Edelbrock performer carb, which is a 625 CFM carb, but went with the Edelbrock Thunder AVS--which is actually just over 650 CFM---best of both worlds.

The Q-jet is a great choice, if you have a solid one to start with.

[jimfulco]

You can't beat a Q-jet for a street-driven car. A local carb shop can rebuild yours for you, and you won't have to worry with recalibrating anything. I had mine done 5 or 6 years ago for $125, and that included new throttle shaft bushings. Might be up to $150 by now, but that's still cheap for a carb that works like brand new.

[Captkaos]

I agree, for carb use with offroading or daily driving you can beat a Q-jet. They can be rebuilt (minus worn bushings) for about $50.

[Pyrotechnic]

Originally Posted by streetstar

Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .

A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .

GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog

Yes the typical Q-Jet CAN flow up to 750 CFM. The way the secondaries are designed though, that doesn't always happen. The secondaries and secondary metering rods on the Q-Jet are designed to flow only as much air and fuel as the motor needs. A 305 or 350 will not pull 750 CFM through the carburetor. They went with this design so a single carb body could cover a large range of displacements and power levels.

[lurch115]

i've messed with / rebuilt just about any and every carb. you could think of and as long as you know a few tricks you can rebuild the stock q-jet and have one heck of a carb. the biggest "problem" with them is that if you leave them sit long enough to dry out the accelerator pump (which is made of rubber like material) also dries out and cracks. Allowing fuel and pressure to get through it....which is why you get the big flat spot in acceleration when you put your foot down quick.... the other issue is with the automatic chokes... edelbrock 1406 is also a good choice

[Zoomad75]

I can say this, Q-jets (when tuned) are extremely reliable. Your hard starting after sitting for a while is probably related to leaks from the float bowl that end up below the carb. This causes one major issue; if it's leaking the float bowl will empty. Since it's empty, it takes more cranking to get the fuel pump to get fuel back up to the carb.

It's an easy fix. Remove the carb. Then remove the throttle body. Once the throttle body is off, you'll see 2 large casting plugs and a couple of smaller ones. If it has been leaking they will be all covered in fuel varnish. Clean the area up really good and then whip up a batch of JB-weld and cover the plugs past the seams. Let it cure overnight before reassembling and putting it back on the truck.

Personally, I'd rebuild the carb at that point since your going to have it halfway apart anyway. The kit is under $30 at most parts stores. If carbs spook you due to the complexity, have it done.

My q-jet in my 75K5 has been rebuilt by a pro (my Dad). No fancy tweaks, just a solid rebuild with being calibrated for my truck. I can leave it alone for a month, hop in kick the throttle a couple of times and it lights right up. Runs great on the highway and off road. Never stumbled on me on the steep stuff.

[kevinr1970]

Originally Posted by jimfulco

I had mine done 5 or 6 years ago for $125, and that included new throttle shaft bushings. Might be up to $150 by now, but that's still cheap for a carb that works like brand new.

I was asking at the dealer for the little connector that goes to the choke on my '86 GMC. They couldn't get it but said their was this old man in an out of the way shop that could probably help me.
I found his shop and he actually had the connector with a wire lead for $2.
I asked how much to rebuild my carb and he said around $380!
I was thinking I would buy a new one instead but maybe I should just find another carb guy?

[jimfulco]

Bet the dealer was gonna farm it out anyway. Look around for a carb shop, or maybe an automotive electric shop that has a sharp carb guy like the one we have around here.

[slugish]

[QUOTE=piecesparts;2361365]

Originally Posted by streetstar

You are absolutely right in your assmptions that an engine has to be fed according to the demand. However for everyday street driven vehicles, the overcarburetion of a 750 will (and believe me, I have seen it) cause a slobbering problem at the stoplights. Your top end will be EXCELLENT but your daily drivving will be poor. The Q-Jet has small primaries and then transition to the secondaries which gives the 750 effect on them. Where a Holley, Edelbrock or Carter square bore four barrel has a slightly larger primary when it is a 750 and that is detrimental to daily driving.

This all depends on a couple of other factors 1) weight of the vehicle--a truck is heavier than a Camaro, so it will respond more sluggishly, unless really geared low. 2) the gear ing is the next thing---people of today are trying to get the gearing high enough to keep the RPMs down, that does not work well with a larger bore carb. 3) The 750 will plate out residue on the intake valves as it works in daily driving and cause more sluggish response as time goes on (seen the effects in a machine shop atmosphere.

Holley and Edelbrock corporations; both will tell you to stay at or below a 650 CFM on a 350 motor and even a 383, if it is street driven; to keep the air flow up and the efficiency of the carb working for you, that way the high velocity will make up for the heavier vehicle weight. Granted, my 383 ran hard all the way up to 6000 RPM with the 750, but I could not get the thing to work right on the street--I had to make a decision, so I did not go to the Edelbrock performer carb, which is a 625 CFM carb, but went with the Edelbrock Thunder AVS--which is actually just over 650 CFM---best of both worlds.

The Q-jet is a great choice, if you have a solid one to start with.

Ithink you are right on the money peicesparts with your carb knowledge . I have a mildly built 400 with a holly 650 doble pumper. In your opion , is this agood choice. Also having continued problems fouling plugs. Take out & they smell of gas with black sooty tips. Person that built engine thinks by pumping the gas to get it started (no choke ) maybe gas fouling the plugs. Have put new hot plugs in now & keeping an eye on , & not pumping as hard when trying to start . Any feedback would be great .

[Billla]

Been posted a million times, but:

CFM = ((CI x RPM)/3456) x VE; VE for a stock engine is around 75% (optimistic).

This means for a square bore you don't need the secondaries until 4000 RPM, and you'd have to turn 8K to need more than 600 CFM

Another vote for a good overhaul on your existing Q-Jet. They're great carbs and typically just need a little TLC. The only problem is tuneability - there just isn't great availability on jets and rods any more After the Q-Jet, any good vacuum secondary carb of 600-650 CFM is a good choice.