318 carb choice, holley only.

[S.I. Coronet]

I have a .030 318, flattops, comp cam 470/270, Performer intake.
Its got a 750 vacuum on it now but its tired and wearing out.
Im going to buy either a 650 DP or a 600 vacuum.
Whats it going to be????
Without too much fanfare whats your alls opinion???

 

[rumblefish360]

Dp's work well with manual trans cars or high stall machines. The 600VC is fine.
I myself would look at a 650 VC since it'll be a new carb.

 

[S.I. Coronet]

Ya know , I looked at ebay dealers for a carb and by the time I either pay the over priced shipping or have to rebuild it and have as much it it as a new one I think I'll just buy a new 600 From Summit.
What about those new non adjustable float ones they have now???

 

[S.I. Coronet]

I played it safe and bought a new one from Summit.
Its a polished 600 vacuum secondary.
The old 750 would spew fuel into all 4 barrels after I turned the car off????

 

[OLD318]

I had an old MP P4529116 aluminum 4 barrel intake for years and never put it on.
Just stuck with my old 318 iron intake carter 2bbl. I went ahead and bought a new
shiny 600CFM Holley electric Choke, Vacuum secondaries and put it on.
What an improvement! I wish I had done this 10 years ago....

IMHO, with stock heads, and a stock camshaft, The 600 CFG Holley is the better choice. Double Pumpers or anything bigger is not going to be utilized effectively...

The 600 Univerasal is relatively cheap and easy to put on.
Holley offers a smaller one which cost more than the 600...

You do however have to get the 4 barrel throttle linkage from a donor car.
along with the intake mounting bracket. I used a 4 barrel 340 heated air cleaner
from a 73 Duster. The entire setup is turnkey at this point, I'm very happy with it!

Best of luck...

 

[S.I. Coronet]

I have the throttle and trans cable from Extreme motor sports and they work real well.
I think this 750 is just plain wore out just like the rest of the old engine was.
My favorite carb is a Holley and when they start to act up too much they need replaced instead of rebuilding them 3xs a year!!!

 

[Meep-Meep]

The 600 Vac secondary was a good choice.

 

[S.I. Coronet]

Well this is turning into a blog!
Got the carb and it misses so bad at idle and stubles and dies when I give it gas.
I adjusted the air mixture with a gauge and checked for vacuum leaks but all is fine.
This is one of those you can't adjust the floats.
I did get it to run a little better by adjusting the pump arm but its studdering going down the road and it didnt do that before.
Anyway i did what I wanted to in the first place and ordered me a 650 DP and the matching power valves I need, now I can send back the other one and get a refund and wont be out too much more. Gesssss!

 

[S.I. Coronet]

Well Im at my wits end with the continuing saga trying to get a carb to work.
i just got a new 650DP Holley and from the beginning just like the the 600 it has a dead spot right at idle and runs rough and/or stalls when i give it gas.
i changed the power valve, front squiter, front pump gasket, adjusted the arm up and down and got different results but mostley back to dead spot stumble.
I made sure it has gas in the tank.
If I looked down at the squirter and would give it gas and hardly any comes out, so i adjust the pump arm spring until there was nothing left to adjust and the same thing from top to bottom?
AM I ready for an Edelbrock performer carb and call it a day or what???

 

[Manifold]

Maybe I can help:

- I'm suspecting that the primary throttle shaft is rotated too far and exposing too much of the transfer slots. How many turns from closed do you have the idle adjustment screw?
- If it is more than about one full turn open, then you need to open up the secondaries a touch with the stop screw. This will allow you to close up the primary some, preferably to the point that the idle adjustment screw will idle a bit too low when the screw is backed all the way out, allowing you to only open up the primaries a little to achieve the desired idle RPMs.
- How far out to you have the idle fuel feed screws on the primary metering block (assuming you do not have a four corner idle)? From what I read, I would guess you are using a vacuum gauge to make this adjustment. Get them to make max vacuum then go back to resetting the throttle blades (may have to open up the secondaries a touch more to get the primary throttle blades back in the sweet spot).

I'd go back to the stock squirter and a middle of the road/the stock pump cam. You should not be trying to make changes at the screw portion of the accelerator pump linkage. Get that set back to factory specs - make sure when the linkage is fully open that the nut comes off the linkage .015". If you can't get the linkage to work right (squirt gas right at the moment the throttle begins to open and have the .015"), you may have to tweak that linkage (I hope it's metal and not plastic).

Good luck!

 

[1badgtx]

Manifold is probably right!!
Petty Blue 67 GTX

 

[Manifold]

My above suggestions were for the dead spot. I have a few suggestions for the accelerator pump circuit:

- When you use your finger to push down on the primary accelerator pump diaphragm arm, do you get a good, solid squirt or is it just a dribble (or whatever you're experiencing)? Don't do this too much as you run the risk of damaging the diaphragm.
-- If solid, work backwards in the circuit to fix. Look at pump cam installation (make sure it's installed on the #1 hole and not the #2 hole), override spring adjustment is correct, possibly slightly bending the arm to take up slack (then reset the override spring adjustment), etc. Movement should happen instantaneous when the primary throttle shaft begins to move.
-- If a dribble, work forward in the circuit. Check the front pump diaphragm (make sure it isn't leaking, torn - sounds like you've already done this), make sure you didn't install a bowl/metering block gasket backwards (though nowadays I don't think they design them so there is a backwards) or that the gasket is blocking the fuel passage for the squirter, make sure the squirter needle valve is present [this might be your problem - this needle ensures fuel is always present at the squirter] which is installed below the squirter [if you turned the carb upside down to jiggle the squirter out of the choke horn, this little guy would have fallen out], and take a peek into the squirter nozzles themselves to see if they're clogged (use either the appropriately sized drill bit or a wire brush bristle to physically clear the nozzles).

Let us know how it's going. Best of luck!

 

[S.I. Coronet]

Today I tested the fuel pump pressure and I got 8lbs.
I guess I'll take the carb off and check the front pump diaphragm.

 

[Manifold]

Today I tested the fuel pump pressure and I got 8lbs.
I guess I'll take the carb off and check the front pump diaphragm.

If it were me, I'd bring that pressure down to 5-6.

While you have the carb off, check to see how much of the transfer fuel slots are exposed at the current idle setting. You only want about .020" exposed at idle - it should look like a tiny square and not a rectangle when properly exposed.