another carb question

[coronet66]

I have a 66 coronet 500 , it has a 383 and 4 spd. Bottom end is stock but it has a comp cam, 256 & 260 @.050- 521 & 524 lift. The heads and valves have been totally worked and roller rockers. Has a edelbrock dual plane intake and I put an edelbrock 750 cfm carb on. The car hasn't run right with that carb yet. What would be the best carb to use for this setup? Any help would be greatly appreciated.

 

[RedHot67]

Hi,

I`d stay below 700cfm and go for mechanical secondaries + annular boosters:

http://www.quickfueltechnology.com/...treet-carburetor-650-cfm-annular-booster.html

That one will wake up your engine, very good carb!!!

I have a 680cfm Quick Fuel on my 440/727, really kicks butt.

Dan

 

[moparmarks]

Did you do any tuning of the carb or is it just out of the box?

 

[rsd859]

I was thinking a 750 would be better for a 383/400. I have a 400 with a 650 on it and was thinking about going with a bigger carb. I am going to look into the quick fuel.

I think moparmarks onto something, with a eddy you may have to change some metering rod springs around to get the best performance for you application. Rich

 

[moparmarks]

Any aftermarket carb needs to be tuned for the car.
I have alot of "free" Holleys given to me cause they didn't run good "out of the box". Especially here at 4500'.
I run 750's on my 440 street motors for the most part.
As RedHot stated that 650 would a good carb for that 383 if you want to dilly out the dough.

 

[coronet66]

I did have to adjust the float and took apart and cleaned it. I've never changed any jets. the main problem is hard starts after it's warm and a flat spot (hesitation) at about 3500 rpm. I forgot to mention, this was a rebuilt carb not new. Don't know if that makes a difference

 

[RustyRatRod]

Are you sure on those cam specs? Which part number is that?

 

[rsd859]

A phenolic carb spacer should solve your hard start problem and is the flat spot during idle or under load?

 

[RedHot67]

Did you do any tuning of the carb or is it just out of the box?

I only had to adjust the idle mixture screws, even the factory jetting was according to my AFR perfect:

http://www.youtube.com/watch?v=PAi76EfkCxw (was my last car with a 580cfm Quick Fuel)

Also the cold start idle was perfectly pre adjusted, never had such a nice carb before, no worries at all.

- - - Updated - - -

I did have to adjust the float and took apart and cleaned it. I've never changed any jets. the main problem is hard starts after it's warm and a flat spot (hesitation) at about 3500 rpm. I forgot to mention, this was a rebuilt carb not new. Don't know if that makes a difference

Edelbrock is know for a too lean mixture at higher rpms which seriously can damage the engine.
If you have hard starts when the engine is warm, check your fuel line, replace metal lines with rubber hoses and use a plastic filter :icon_winkle:

 

[coronet66]

Under load, about 3500 rpm it just goes flat for a second and then picks back up.

- - - Updated - - -

Are you sure on those cam specs? Which part number is that?

Yea, I have the CRB XE274H-10 with 1.6 rocker. Thats the specs they said it would be with those rockers.

 

[RustyRatRod]

Here's your cam.

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=708&sb=2

I don't know where you're comin up with them duration numbers. That's what was throwin me.

 

[coronet66]

Here's your cam.

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=708&sb=2

I don't know where you're comin up with them duration numbers. That's what was throwin me.

I was told that if I used the 1.6 rockers instead of the 1.5 it would change the lift. I'm not a motor guru so thats the specs the guy told me.
You seem to know a lot about motors so what is your feeling on the carb? Do you think I should replace the edelbrock with a different carb and if so which do you recommend

 

[vintage chromoly]

Did you check your timing?

You really need to start there.

 

[coronet66]

Yea the timing isn't the problem. I think being a rebuilt carb something just isn't right with it. Any body else have any carbs to recommend?

 

[67 coronet]

a 650 cfm carb will pull a mild street 383 to 5800 rpms easily.try to keep the carb as small as is efficient for the street in order to keep signal higher.also,if you go away from edelbrock,try to use a vacuum secondary design.they are much more streetable then mechanical secondaries on a street motor.not a very brand specific guy,so i have no exact carb in mind.

 

[caveman85635]

a 650 cfm carb will pull a mild street 383 to 5800 rpms easily.try to keep the carb as small as is efficient for the street in order to keep signal higher.also,if you go away from edelbrock,try to use a vacuum secondary design.they are much more streetable then mechanical secondaries on a street motor.not a very brand specific guy,so i have no exact carb in mind.

My RR is 383 4-speed with a 650 Holley and a Holley Street Dominator manifold. I run mine up to 6,500 rpm regularly and there seems to be plenty of carburetor.

 

[Meep-Meep]

That big cam on a stock bottom end? Do you have any idea what your compression is? If you are running stock for 66 compression you are likely to not even have 10:1. All your carb problems are due to that cam. Put in a smaller cam with an earlier intake valve closing point and less overlap and gain some cylinder pressure and vacuum.

 

[RustyRatRod]

Meep-Meep is right....BUT, the low compression/big cam combo CAN be made to run well, although it will not be as powerful as a smaller cam with the same compression, or more compression and the same cam.

Here's the reason. The Edelbrock carburetors use metering rods. Metering rods operate off of vacuum signal. That camshaft doesn't have enough vacuum signal at idle for the metering rods to operate correctly. You can get a spring kit and TRY to tune the carburetor to the cam, but I suspect it is out of the range of a spring kit.

My advice would be to get a Holley 600 vacuum secondary carburetor. You will be much happier even though the carburetor is smaller. A smaller carburetor will always work out much better than one that's too big. Also, since the Holley lacks metering rods, it is much more tunable with a low vacuum signal. If you have a friend that knows about the Edelbrock carburetors, or want to give it whirl yourself, I am sure there's room for improvement with what you have, I just don't know how much. I KNOW a Holley would make it run pretty good.

Changing the camshaft would be the ultimate way to correct the problem, but if you're constrained by budget, it might not be the best way for you. I think I would try tuning the Edelbrock first. That would be the cheapest thing, and might actually end up working.

Here you go.

http://www.ebay.com/itm/Carter-AFB-...Parts_Accessories&hash=item2a2a4572fd&vxp=mtr

That's a CHEAP metering rod spring kit. They actually go down farther than I thought in vacuum signal. What you need to do is see where your vacuum is idling. I don't know a lot about tuning Edelbrock/Carter AFB types, but here is a nice article about it. I just never have liked them, but that doesn't mean they aren't good units. Good luck.

http://www.carcraft.com/techarticles/carb_tuning/

 

[68 Sport Satellite]

On my 451 stroker build I want to get a Quickfuel carb also. Talked to several quickfuel users and Quickfuel themselves. Have narrowed it down to their street series, either the vacuum secondary 735cfm or the mechanical secondary with annular boosters 750cfm. I know the vacuum secondaries being best for a heavy street car automatic is the consensus, but several people, Quickfuel included, say the annular booster mechanical secondary carb will work great on my motor. Don't think you can get vacuum secondary carb with annular boosters.

Meep-Meep is right....BUT, the low compression/big cam combo CAN be made to run well, although it will not be as powerful as a smaller cam with the same compression, or more compression and the same cam.

Here's the reason. The Edelbrock carburetors use metering rods. Metering rods operate off of vacuum signal. That camshaft doesn't have enough vacuum signal at idle for the metering rods to operate correctly. You can get a spring kit and TRY to tune the carburetor to the cam, but I suspect it is out of the range of a spring kit.

My advice would be to get a Holley 600 vacuum secondary carburetor. You will be much happier even though the carburetor is smaller. A smaller carburetor will always work out much better than one that's too big. Also, since the Holley lacks metering rods, it is much more tunable with a low vacuum signal. If you have a friend that knows about the Edelbrock carburetors, or want to give it whirl yourself, I am sure there's room for improvement with what you have, I just don't know how much. I KNOW a Holley would make it run pretty good.

Changing the camshaft would be the ultimate way to correct the problem, but if you're constrained by budget, it might not be the best way for you. I think I would try tuning the Edelbrock first. That would be the cheapest thing, and might actually end up working.

Here you go.

http://www.ebay.com/itm/Carter-AFB-...Parts_Accessories&hash=item2a2a4572fd&vxp=mtr

That's a CHEAP metering rod spring kit. They actually go down farther than I thought in vacuum signal. What you need to do is see where your vacuum is idling. I don't know a lot about tuning Edelbrock/Carter AFB types, but here is a nice article about it. I just never have liked them, but that doesn't mean they aren't good units. Good luck.

http://www.carcraft.com/techarticles/carb_tuning/

 

[Meep-Meep]

Before you go spending the money on that I'd start with the known working 650 AFB you already own or one of my 750's. You can always improve later, but I bet you will be quite surprised how well that AFB will work on a properly designed engine. My 440 ran it's best (so far) with a 750 AFB on a stock iron intake!