Carb Issues Poor idle after warm up?

[trndkll67]

I just dropped a new 302 HO in with 351 firing order into my 67 coupe. Then I found a brand new Edelbrock 600cfm (#1400) carb to replace the old tired one (600cfm #1406). (Note: The #1400 is specifically listed for a chevy but the only difference I can tell is that the #1400 has an unplugged (open) carburetor bowl vent tube and the #1406 comes with the ford linkage adapter. I popped the #1400 on, everything lined up perfectly(didn't even need the linkage adapter) and I plugged the carb bowl vent with rubber vaccum fitting. It started great and runs great for about 1 mile. Then, when I pull to a stop, the idle is so inconsistent, it barely stays running. Yes, it has even stalled a few times at the stop light/sign. If I park her overnight, and fire it up the next day, the same thing....runs great at first, then get choppy.

I have swapped out the metering rods with almost 8 sets(smaller and larger diameters), some run ok, other cause knocking and pinging. My best luck was with the 073x042 rods(Edel #1455), but the idle issues are still there. I've used some carb spray and can't find any leaks to speak of.

This is all I know to check. Could this be an electric choke issue? Could it be getting flooded at high speeds so at idle it is choked with extra fuel? Could it be a vacuum issue? Any help and advice on what to check/how to check would be much appreciated! Thanks!

[mustangII460]

Have you adjusted the air idle screws.

What PSI fuel pump.

[trndkll67]

I've adjusted the idle screws incrementally from 1/2 out to 4 turns out and it doesn't seem to help much; still the same problems.


I believe it has a stock 302 fuel pump, around 7psi.

[bmxmon]

I was thinking your choke. Once it gets warmed up/runs crappy you cant tune it to run decent again?

[goodyear1984]

when it runs crappy did u look to see the choke position?so this was a brand new in box unit?does it only run crappy at an idel or driving it too?...i would run it and when it starts to act up look and see where the choke position is ,should be open if its warm...if it is opened look to see if the fuel is dripping out or if its got a nice flow..also what are ur cam specs and is ur timming set right...good luck man let us know how u make out

[trndkll67]

Sorry for the delayed response, been out of town....

The cam specs are:

Intake 448
Exhaust 472

Duration .050
204 Intake
214 Exhaust

I replaced the old 1406 with the Edelbrock 1400 600cfm. I got some flack from edelbrock becasue this carb is "prescribed" for a SB chevy, BUT its the exact same as a the 1406 except with no linkage adapter. I installed the linkage adapter and still have the same problems. Edelbrock says I can't tune it for the 302 except by trial-and-error. I thinks thats BS, but what do I know!

Its still running poor at warm idle, I have adjusted the high idle screw and haven't noticed much difference. I've got the choke set at "one notch forward". Should I toss it and a get a 1406, or go with something larger (>650cfm)?

[Elvis]

Well, I just put the same carb on my 302 and it runs great right out of the box. The automatic choke is 1 notch right of centre. I have my choke wire hooked up to the "I" pole on the solenoid. Perhaps you could check that or the ground. E.

[trndkll67]

Elvis:
Do you have a 1406 or a 1400? What rod size are you using? I'll try the choke wire trick; it's currently grounded to the back of the carb; what problems would that indicate if "your way" works? I guess a bad ground?

[Elvis]

Sorry, I misunderstood. Mine is a 1406. You should have a red and a black wire from the choke. The black should be grounded to the carb base and the red goes to the power source. As I stated, mine goes to the "I" pole on the solenoid. Good luck. E.

[trndkll67]

Elvis:

Ok, that's basically what I had before, except my ground wire went to the back of the carb. Red to the power.

I'm just concerned the rebuilt 1406 isn't getting the engine enough fuel. I figured the brand new 1400 (being the same size) out-of-the-box would be a better indicator of if that carb size is "big enough" but the result was no better. I'll give edelbrock a call and see what they reccommend...

Thanks...

[Gearhead999]

The size of the carbs you're talking about aren't going to change the idle of the engine.

Have you checked for a vacumn leak?? Maybe pwr. brake booster, vac. advance, etc. Or maybe the intake manifold gaskets are leaking.

What type of vacumn do you pull at idle?? Where is the timing?? The float level will also effect the hot idle. This type stuff effects the idle quality also.

[trndkll67]

Gearhead:

Both ports on the 1400 are timed vaccum. On the Pasenger side I pull 15psi. On the driver side I pull around 1psi. Not sure why the big difference. The distributor advance tube currently goes to the passenger side.

The float levels out-of-the-box were set at 7/16". Timing was set by my mechanic when the engine was installed. It is correct for the 302 with the 351w cam.

One thing to add: I am getting fuel flow at idle thru the front two venturis; I got the impression from Edelbrock that this is bad (a source of potential flooding). So I've relaxed the edle speed screw to see if that helps....I'll let you know.