Help! 64 vette 327 300hp carb replacement??

[hokie04]

The Carter AFB on my 327 300hp has been rebuilt at least once and now is very unstable gas and vaccum wise. What do you recommend as a good replacement carb and CFM? And are there any that would take the stock air cleaner 4 1/2 inch throat. I looked at the Elebrock AFB but the throat size is 5 1/4. Also the gas is getting very hot and I have the stock cast iron intake should I replace it with an alum. one. What is everyone else doing??

 

[Hib Halverson]

If keeping the engine original is not necessary, I'd replace the intake manifold with an Edelbrock Performer and add an Edelbrock Quadrajet.

For a 327/300 the Quadrajet is the best carburetor choice for performance, driveability and fuel economy.

 

[hokie04]

If keeping the engine original is not necessary, I'd replace the intake manifold with an Edelbrock Performer and add an Edelbrock Quadrajet.

For a 327/300 the Quadrajet is the best carburetor choice for performance, driveability and fuel economy.

Thanks for you input! What CFM would you recommend and do I have to worry about hood clearances?

 

[Hib Halverson]

CFM is not really an issue with QJs. Most are 750 but there were a few Buicks from the early-mid-70s with 800s.

The QJ is an air-valve secondary carb so, even though it's max CFM is 750, it probably will not flow that much on a 327.

As for hood clearance, you'll have to check with Edelbrock on that. In addition, hood clearance will depend on the air filter assembly you choose.

 

[magicv8]

IMO the Carter AFB on your car is the easiest to maintain and the most stable at idle, under acceleration, and cruising. I don't believe any other 4venturi carb will accept the factory air cleaner, but you might try screwing the Carter air horn onto an edelbrock base - if you can get a friend to loan you one.

IMO 90% of all fuel problems are really ignition problems. If you decide to get rid of your AFB, send me an email.

 

[Hib Halverson]

The QJ obviously will not accept the air cleaner on a Carter, but there's an easy way out. Use the air cleaner off a 66 or 67 with Quadrajet.

I'm not sure I agree with the statement above about the Carter being "most stable at..."

Reality is that the reason GM stopped using Carter AFBs at the end of MY65 is that the Rochester Quadrajet performed better, offered improved driveability and better fuel economy than anything Carter could bring to the table. Plus it dispensed with the AFBs very poor float bowl design.

The reason anyhing that road raced after 1965 had a Holley on it was that the AFB had poor fuel control under hard acceleration and braking. That is why, once Holley's 4150 design arrived, racers ditched AFBs in droves. Holley adding center-hung float bowls a year or so later, that was the kiss-of-death for the AFB.

If the car needs to be original, stick with the Carter, if originality is not an issue, for a 327/300, the Quadrajet, with proper tuning, is the best choice when performance, drivability and economy are the important issues.

 

[magicv8]

The QJ obviously will not accept the air cleaner on a Carter, but there's an easy way out. Use the air cleaner off a 66 or 67 with Quadrajet.

66 and 67 Corvettes only used Holley carbs with the larger air horn openings.

 

[Grizzly]

The Carter AFB on my 327 300hp has been rebuilt at least once and now is very unstable gas and vaccum wise. What do you recommend as a good replacement carb and CFM? And are there any that would take the stock air cleaner 4 1/2 inch throat. I looked at the Elebrock AFB but the throat size is 5 1/4. Also the gas is getting very hot and I have the stock cast iron intake should I replace it with an alum. one. What is everyone else doing??

For what it's worth I put a 650 Barry Grant on my '67 300hp. Just bolted it on and made up a new fuel line, adjusted the idle, and it runs like a champ. Called BG and told them what I needed and they gave me a part number that I gave to Jegs. Same air cleaner. In few days back on the road.

No Pain .............................. Griz

 

[magicv8]

Ya got me all excited about a carb with a 4.5 inch air horn untill I called Barry Grant tech support - and found out it needs a5.25 inch opening in the air cleaner - which your 67 has, since it came with a Holley. I should have noted that you have a 67, but I got tooexcited - oh well. Maybe a 67 air cleaner is also needed for the swap.....

 

[Hib Halverson]

66 and 67 Corvettes only used Holley carbs with the larger air horn openings.

You are right.
Rochesters may have been on other GM products of that period but were NOT used on Corvette in MY66 or 67. It wasn't until MY68 QJs were used on Corvette.

I apologize for any confusion my earlier post may have caused.

But, the fact remains that for a 327/300 where originality is not an issue, an Edelbrock Performer with a Quadrajet is the best carburetor choice for performance, driveability and fuel economy. No doubt, there are a number of air cleaner choices for that configuration which will work, as C2 has more hood clearance does C3 and that manifold/carb pairing is common on C3s.

 

[hokie04]

You are right.
Rochesters may have been on other GM products of that period but were NOT used on Corvette in MY66 or 67. It wasn't until MY68 QJs were used on Corvette.

I apologize for any confusion my earlier post may have caused.

But, the fact remains that for a 327/300 where originality is not an issue, an Edelbrock Performer with a Quadrajet is the best carburetor choice for performance, driveability and fuel economy. No doubt, there are a number of air cleaner choices for that configuration which will work, as C2 has more hood clearance does C3 and that manifold/carb pairing is common on C3s.

I have decided to give the AFB a try before I go to non stock applications. I just ordered a complete rebuild kit. Do you have any suggestion on how to keep this carb from get so hot? The 300hp has a spacer and stainless steel baffle plate but it still doesn't get it done. I noticed one of the two exhaust holes in the intake was plugged. Would plugging the other one do it. I don't care about winter weather since the car will be stored. Are there any other type spacers out today that might be better?

 

[LVMYVT76]

Should you pull the intake and have it cleaned to make sure all the heat passage is open?? It worked out of the factory, it should work now if everything is correct.

 

[magicv8]

I noticed one of the two exhaust holes in the intake was plugged. Would plugging the other one do it. I don't care about winter weather since the car will be stored. Are there any other type spacers out today that might be better?

I live in Illinois and even in zero weather my AFB does not need a choke or heat passages to start and warm up the engine - I simply press the pedal down 2 or 3 times to start it in cold weather. It runs fine after that.

With modern fuel formulation, I found that the AFB does not need the manifold heat applied through the bottom of the factory phenolic carb spacer to the stainless heat shield. Years ago, I removed the carb, tapped the holes in the intake that provide exhaust gas, and inserted hex key plugs. Others have successfully driven small "soft plugs" into the holes to plug them. With the holes plugged and my heat riser butterfly removed, the gasoline fumes in the garage are minimized after hot shut down, and performance is better in hot weather.

IMO 90% of all carb problems are really ignition problems. One of the things I did to allow me some freedom to set the advance to suit the gasoline, was to install an Accel adjustable vacuum advance. After a few runs accelerating between expressway on ramps with an allen wrench in my hands, my timing problems disappeared.

good luck......

 

[hokie04]

I have rebuilt the AFB and it looked like new inside other than the float settings were not even close. We found a crack in the spacer plate that the baffle and carb sit on. This may be the problem. Question I still want to plug the 7/16 exhaust hole in the intake and a local parts store told me to just use a 7/16 freeze plug. How do you think this would hold up?? I don't have a die and tap set and don't want to remove the intake to take to someone to do.

 

[magicv8]

I believe johnz onceposted a pic of an intake with freeze plugs - maybe he will post an opinion. My manifold has threaded plugs.

IMO it should last several years before corrosion eats them, then you just pop in new ones.

 

[JohnZ]

Here's a 300hp AFB iron intake with the two exhaust passages plugged with cup plugs - don't recall the size, but I think they were 7/16"; measure yours and get the corresponding plugs - they're in the Dorman assortment at your auto parts store.

 

[hokie04]

They are 7/16 like you said but I can only find them in steel plugs. I wish I could find them in SS. How long ago did you put yours in and how are they holding up? Part of me is telling me to just tap the holes and be done with it. What are your thoughts.

 

[JohnZ]

They are 7/16 like you said but I can only find them in steel plugs. I wish I could find them in SS. How long ago did you put yours in and how are they holding up? Part of me is telling me to just tap the holes and be done with it. What are your thoughts.

No need for stainless - regular steel plugs will work fine. I've also tapped the holes and used allen-head plugs.

 

[Ron Miller]

I have rebuilt the AFB and it looked like new inside other than the float settings were not even close. We found a crack in the spacer plate that the baffle and carb sit on. This may be the problem. Question I still want to plug the 7/16 exhaust hole in the intake and a local parts store told me to just use a 7/16 freeze plug. How do you think this would hold up?? I don't have a die and tap set and don't want to remove the intake to take to someone to do.

You don't have to have a tap & die set, you can buy one properly sized tap for $3-$4 and carefully use a wrench to tap enough of the hole to insert an allen head screw. You won't have to tap all the way through, just enough to thread the allen screw into.

Use some heavy grease on the tap to catch the chips. I've done mine both ways (with the tap and with the freeze plugs), and I feel much safer with the tap method, never know when or what might upset the freeze plug and let it drop into the intake.

Also, if you've never used a tap, you don't need to continually advance the tap in the hole. It needs to turn 1/4 to 1/2 round, then back up 1/4 or so turn before advancing again. This helps break the thread chips loose and will keep the tap from seizing or breaking.

My suggestion,

 

[hokie04]

Thanks everyone for all the help! I went the freeze plug method on Saturday and the car is idling great and the carb seems cooler. So I guess now time will tell....