edlebrock 600 on 390

[wayne]

A lot ways to do this check some of this out.


http://www.gofastforless.com/ignition/tfi.htm

[stubbie]

600 should be enough for a standard 390. There is a formula on the net to work out you carb size.
CFM = Cubic Inches x RPM x Volumetric Efficiency ÷ 3456. Any ordinary stock engine will have a volumetric efficiency of about 80%

[cammerfe]

Back about a zillion years ago I did a rework on the 302 2-barrel engine in my '72 E-150. I put on an Ebock Sp-2P manifold, a Holley 6708 carb, a mild cam, and a set of headers. Basic feel, I doubled the usable horsepressure and increased highway MPG from about 12 to 18 or a bit better.

I have a friend who also had an E-150. We swapped in a 351 Windsor with a couple of changes. My van would easily outrun his.

The Holley 6708 has smaller primaries and larger secondaries than the usual list 650 DP. And it uses a choke cable. Unfortunately, they're no longer made, but you can find remans on the 'net. It's a great carb for the sort of use I made of it. (But likely not as good as EFI.)

KS

[frnkeore]

Keith, there is another carb, similar to your 6708 but, with much larger venturi. It has the 600 primary and 850 secondary's. It cam on the 383 Mopar engines. It's list is 4218. I think it would be perfect for a 390 if, you could find one.

It's one of the carbs that I will try on my 419.

[My427stang]

I think this is a tuning or setup problem that may or may not be fixed with parts replacement.

A 600 Edelbrock will be happy as a clam on a 390, even a healthy-ish street one.  It won't make the same power as a equal Holley, but by no means should it be choking the engine and going pig rich on the plugs and blowing black smoke.  In fact, they tend to do very little wrong other than being down a little bit on power

First - Make sure the air cleaner lid isn't slammed against the top, filter isn't plugged, make sure no linkage is binding the choke, and the choke is working properly.  It needs to be open when hot and not too tight when cold, plenty of videos on You tube.  Even if adjusted correctly, it needs to be working too, wide open warm, and not able to close under acceleration.  Choke thermostats do go bad, and wiring can be incorrect letting it close on you

Second - I'd put the carb back to stock with a full rebuild, carefully make sure all adjustments are right and linkage doesn't bind on intake etc.  Don't assume anything, and be gentle with the parts, check all the numbers of parts, make sure it hasn't been modified

My hunch tells me those two things will do it, however, next make sure the engine has heat, run a thermostat.  Then look at the ignition, what it is means less than if it's working right.  You should have a mean blue spark from an HEI, if it is anyhting less than that, look closely at coil, module, grounds etc.  The ignition could be bad as a small change in a/f generally does not bring you from pig rich to surge FWIW, HEIs can generally handle it, but I tend to not go big on gaps, although some claim wild benefits, typically, .035 is easier on ignition parts and will fight you less with misfire on a marginal ignition.  Likely NOT your problem, but my technique is .035 for most builds

I could see you buying a 40 dollar carb kit, or a coil/module, but I really don't see this being a brand/parts mismatch, requiring a new carb and ignition, you are simply having a tuning or malfunction problem with the parts you have

[390owner]

I just cleaned the air filter (k and n). Nothing is binding. The choke is tied open.  I am  going to double check all that you mentioned and look at the fuel pressure too Thanks for all the replies

[My427stang]

Fuel pressure is a good call, I agree with that if i didn't have it in there

Some other thoughts, looking back, what have you fixed from past problems?

I see you had:

1 - Oil use from the PCV (which shouldn't be an issue if low blow by on a fresh engine and a correctly configured PCV)  Eliminating it is sort of a band aid
2 - High but unsteady vacuum reading
3 - Timing issues, to include being very sluggish and not running your vacuum advance

I read a few times that 20 years ago the shop built you a good one, but this one seems like it isn't as good as the last one.  Have you picked away and found the cause of the earlier issues?

[GerryP]

If you want to run a spreadbore carburetor you can do it with Quadrajets, Thermoquads, Autolite 4300/4350, many of the AFBs, and Holley as Q-jet replacements in both vacuum and double pumpers in 650-800 CFM.  They work great.  The downside is you have to use an adapter to use them on non spreadbore intakes.

[plovett]

A comment not likely related to the original issue:  I personally wouldn't run the plug gap that wide even with HEI.  Just my opinion, but I have not ever seen any measurable gain by doing that and I have seen issues caused by it.  I like 0.035".  I even even do that on my "modern" 2000 Saturn.  I could see going to 0.040", but not more. 

I also don't think a 600 cfm Edelbrock is too small for a mild 390.  It may not be optimal for the last couple of horsepower, but it will work fine.  If I was the slightest bit concerned in that respect, I would just put a 1/2" open spacer under it.  It will effectively increase the carb size, and insulate from heat, to boot.

So I am guessing the guys advocating making sure the fuel pressure is right on, are right on.

JMO,

paul

[gdaddy01]

like was said above , check the breather lid , maybe already said , make sure the bowl vent is open and far enough from the breather lid and  or the vacuum lines are hooked up in the correct locations . 

[390owner]

This new 390 is now running as good as the first one I had built years ago. I have the vacuum advanced hooked up now.I also have a spacer under my carb. It is a carbon fiber one.

[plovett]

This new 390 is now running as good as the first one I had built years ago. I have the vacuum advanced hooked up now.I also have a spacer under my carb. It is a carbon fiber one.

Was there anything in particular you think fixed it?

[390owner]

Running higher octane gas, played with the timing.

[fryedaddy]

i knew the better gas would help.my dad had a 63 1/2 galaxie 390 and he was so cheap he ran the cheapest gas he could find in it.it still ran ok but it pinged on hills and you could tell it needed better fuel.he later gave it to me and i always ran premium in it and it would fly.