Holley 390 running way rich

[clutchdust]

For the most part I've been really happy with the way my car has been running even though I've felt it was running rich the whole time. Pulling plugs every couple hundred miles and they're coated with a pretty thick layer of black carbon. Not to mention puffs of black smoke just revving it in neutral

Today, I finally got the O2 sensor connected, at least temporarily, so I can prove my theory. Sure enough, the sensor shows it just about pegged on the rich side under all conditions short of lifting off throttle. In neutral, when I lift off the throttle the meter comes way back, almost (but not all the way) to lean until it hits idle speed and then goes right back to rich. While in gear, lifting off (engine braking) will put it just about in the middle of the "stoch" range.

The only other time it appears to come off full rich is right at throttle tip in and then it goes just to light side of rich. I'm thinking that tells me about the only thing that's right on this set up right now is the pump shot.

So I just put #52 jets in it, it had #54, and that made almost no difference. I have the idle mixture screws turned almost all the way in. I mean literally, I think they're turned out maybe 1/8 turn.

Any thoughts?

[beermanpete]

Smaller main jets.

Check the float levels.

Check the fuel pressure. It should be between 5 and 7.5 PSI

Check the power valves. They go bad easily on Holleys.

Smaller main jets.

[clutchdust]

With you on the main jets.

Pressure is about 6psi

Float level is good.

I'll check PV but this is the newer design with PV protection.

Thing I'm struggling with though is why it's running so rich even on the idle circuit.

Edited October 21, 2011 by clutchdust

[jt1]

Check the air bleeds. You should be able to put your finger over the idle air bleeds and hear the idle rpm change. If not they're stopped up. More initial timing may help, and check to see if the blades are exposing enough of the transfer slot that you're running off the transition circuit.

 

jt

[c6fan]

Sounds like fuel spilling over from a stuck inlet needle on one of the floats.

[ozconnection]

You don't mention what intake manifold you've got the 390 on. That will make a big difference to how you set up your carb.

 

You don't mention how big your cam is or how much vacuum you have at idle. Is the trans. auto or manual?

 

You'll be very surprised at how much driving is done without using the main circuit in the carb. I was shocked when I did some testing a while ago. Changing from #54 to #52 jet size will do very little. What was your stock jet size on your primarys?

 

Your idle air bleeds are possibly too small but if you make them larger you run the risk of going too far and leaning things out too much. Its hard (but not impossible)to put back in what the drill bit has taken out.

 

Float level will make a difference. Do you have an electric pump? It's so easy to check for internal carb leaks with a few feet of hose connected remotely to your carb on a bench with leg supports where the mounting bolts go. Turn your pump on and watch what happens. Lightly bump and move your carb to see how easily fuel will spill into your manifold when you have your carb hooked up and the engine running. Raise or lower your needle and seats/float level accordingly.

 

How is the float level in the secondaries and how far open are they at idle. They contribute to the idle as well, so check 'em.

 

Let us know how you get on.

Edited November 26, 2011 by ozconnection