Need carb advice.

68stang351

Founding Member
May 16, 2002
850
8
39
Savoy TX
Well I know I'm having carb issues, but I'm not really sure what to do here.

After swapping my top end my carb is not set right anymore, but here's the dilemma I'm at now.

I had a stock 69 351w with a 5 speed in my 68 Coupe, and an Edelbrock 1405 600 carb, and it was fine.

Now it has Twisted Wedge heads, and a Comp XE284 cam, and obviously I need to mess with the carb.

Here's the options that I believe I have.

Keep trying to mess with the Edelbrock 600 (I do have a jet/rods/spring kit)
Rebuild the Holley 750 I scored for free and use it (I wonder if the 600 too small for my combo? or if the 750 is too big?)
Or try to get a Holley 650

I guess what I'm wanting to know is 600cfm, 650, or 750?
Holley or Edelbrock???

In either case I will have to learn how to tune these. Well I know how to make adjustments on both, I just don't know what adjustments to make.

I checked the plugs, and they don't look like it's been lean or rich, but something is definitely not right for my new combo with this Eddy 600 carb I have.

So I guess I'm asking for tuning advice and/or carb suggestions. Can anyone help? I'm open to all ideas.
 
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I guess you probably need more info.

While cruising, it kind of surges, and also stumbles going into WOT too. It's okay WOT in 1st and 2nd gears, but has "flat spots" in WOT in a higher gear.

The car currently has 3.50 gears, but will get something more like 4.30's in the future.
 
The 750 Holley is the perfect size for it, if it's a vacuum 750.(and it's in rebuildable condition, if it looks old don't bother with it) A 750 DP will be a little too much cfm at lower rpms (when you nail the go pedal suddenly and open all 4 bbls) The Eddy 600 is definately too small for anything but straight street driving and fuel economy (you obviously didn't build for economy) A 650 Holley DP would be spot on (if you're not concerned about economy), a 80783 Vacuum 650 would also be a good-un, giving both economy and performance, as the secondarys have a metering block so that you can richen up the secondaries for the upper rpms.
 
A friend of mine got me a copy of the Edelbrock "how to tune" DVD. They recommend moving the pump arm, that is on the drivers side from the bottom hole to the top hole to help eliminate that exact problem....You might try that first, then decide.
 
I would rework the Edelbrock and see how that does first.

I think I'll try that, because it won't cost me anything since I already have a calibration kit.

The 750 Holley is the perfect size for it, if it's a vacuum 750.(and it's in rebuildable condition, if it looks old don't bother with it) A 750 DP will be a little too much cfm at lower rpms (when you nail the go pedal suddenly and open all 4 bbls) The Eddy 600 is definately too small for anything but straight street driving and fuel economy (you obviously didn't build for economy) A 650 Holley DP would be spot on (if you're not concerned about economy), a 80783 Vacuum 650 would also be a good-un, giving both economy and performance, as the secondarys have a metering block so that you can richen up the secondaries for the upper rpms.

Thanks! You answered a few questions I had. If I can't work out this Eddelbog then I'll try to score a good deal on a 650 Vacuum.

A friend of mine got me a copy of the Edelbrock "how to tune" DVD. They recommend moving the pump arm, that is on the drivers side from the bottom hole to the top hole to help eliminate that exact problem....You might try that first, then decide.

Thanks man! I hadn't even thought of that!

Great advice from all of you.
Any more?
 
Surging at cruise is a lean condition. You need smaller rod/larger jet combo.

tx65coupe is right, the stumble going WOT needs a bigger shot. Try the first hole on the arm.

DH is rightest. The carb is too small!

I wouldn't run an eddy with that combo anyway. You built that motor for power and that is not where the Eddy carbs shine. 351, heads, cam and you are going to choke it to save buying a new carb???
 
351, heads, cam and you are going to choke it to save buying a new carb???

No, I'm just trying to feel out my options right now. I've pretty much planned on having to buy a new carb but I'm trying to get all the advice I can before I go do that.

I WILL have a new carb, but in the meantime while I'm saving for it I should still try to get the most out of what I have until then right?
 
Instead of buying a new Holley, look for a slightly used second hand Holley. I pick these up for half of what a new one cost, from the guys who "give up" on em. The last one I bought was a nearly new 570 Street Avenger, paid $150 for it on ebay. All I did to it when I got it was put in a new powervalve, just as insurance that the old one was dried out and ruptured. It's been on the job for well over a year now with no problems. I've done the same with several Holleys over the last few years. One was a 3310 750 that was run without tuning (the secondaries were never opened up) and no fuel filter (the primary side inlet filter (behind the inlet fitting inside the bowl opening) This filter was plugged with what looked like red mud. That's why the previous owner "gave up" on it. That's what also told me he never tuned it to where the secondaries opened up, that filter was clean as a whistle. Buy one like this, invest in a quick kit, take the bowls off, change the P/V and accellerator pump diaphram, clean the inlet filters and bolt it back together and then tune it for your motor.
 
you can also buy a reman demon on ebay

here is the perfect carb http://cgi.ebay.com/ebaymotors/MIGH...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories,

every demon I have bought was from that guy remanufactured and they were all perfect and almost perfectly tuned out of the box, I messed with an edelbrock 750 on my 351w over and over I got it pretty spot on, I bought a speed demon 650 reman from that guy and it was like I added efi, better throttle reponse, way more power everywhere and better mpg's, smoother idle even smoother quieter operation. Same on my 408, tried the edel 750 (lots of noise but not power and stumble), the 650 speed demon ran great but not enough for my combo, I spent 725.00 on a prosystems custom built 950hp for my combo (not really impressed except WOT) bought a 750 mighty demon annular from that guy (reman) and low and behold my 408 ran better than ever for over 300.00 cheaper than my custom holley, I installed a wide band 02 sensor and it runs almost right where it should. I can tell you from experience you will not get an edel 600 to run right with your cam and heads no matter what you do. Call demon carbs and ask their recomendation, they know their stuff and demons flow a bit more than same sized holleys and edels thats why you go a bit smaller with a demon, a mighty demon 750 flows about 900 cfm, the annular versions flow slightly less but give big gains in low end TQ and HP. Even though its not the recomended carb a cheaper speed demon will work great on your combo. The mighty demon is much more tunable and has removable air bleeds, I am over carbs and am installing the powerjection efi on my 408 but the demons are the best carbs you can buy for the money, dollar for dollar demon versus holley you get much more for your money with a demon carb.
 
A friend of mine got me a copy of the Edelbrock "how to tune" DVD. They recommend moving the pump arm, that is on the drivers side from the bottom hole to the top hole to help eliminate that exact problem....You might try that first, then decide.

Mine was in the middle. I moved it to the top, and put in the next smaller rods that I had in my kit.

It screams now. Runs like a different car. Haven't done much cruise yet so I'm not sure about how it drives that way. BUT, the plugs electrodes are very white after a hard WOT run, so maybe I should just got to the smallest rods in my kit.
 
Well I know I'm having carb issues, but I'm not really sure what to do here.


Keep trying to mess with the Edelbrock 600 (I do have a jet/rods/spring kit)
Rebuild the Holley 750 I scored for free and use it I checked the plugs, and they don't look like it's been lean or rich, but something is definitely not right for my new combo with this Eddy 600 carb I have.

So I guess I'm asking for tuning advice and/or carb suggestions.

Use the Holley with a rebuild kit and sec spring pack.
Once it is set up it will out perform the Edelbrock.