Holley Street HP carb too rich at idle.

Yes, let's get this out of the way now...750 cfm is too big for my engine.

At idle.

When I get into it, it is not, and performs very well.

But at idle, it is way too rich, burns my eyes. If I lean out the idle mixture anymore, it dies.

All the bleeds etc are swappable on this carb. So, without reading the book (again) and trying from scratch, what should I do to make this thing idle leaner without messing up my top end performance?

 

Or who wants to buy a new carb so I can buy a bolt on TBI setup?

 

Guess adjusting the idle air mixture screws aren't helping? Is it possible they're messed up?

 

I think it is just trying to adjust too big a carb at too little air flow at idle.

If I lean them out more, the low airflow over those big venturis wont keep an idle.

That is my guess...

 

Is this carb a 4-corner idler? Are the secondaries completely closed off at idle? If they aren't it might help if they were...

 

Yes, 4-corner idle. I was just thinking the same thing...

 

Just a thought i have done this before and it has worked.On the secondary throttle side there is a adjusting screw for the throttle blades.You may have to flip the carb over to see it.Open the rear throttle blades a bit.This will let a little more air in without drawing in more fuel and should help clean up the idle.With the size of cam your running it should be idling close to 1000 rpm.Just fine tune the adjustment from there.
As far as messing with air bleeds thats something i have never played with.All my Holleys are way too old to have removable ones

 

With my cam, it SHOULD be idling at 1000, but I keep it down at a nice lopey 650. Might be part of my problem?

But, yeah! That is the kind of stuff I am looking for. It runs GREAT, but just annoying at idle. I cannot see swapping carbs for that.

 

How many turns are your misture screws backed out? Also what size are the idle air bleeds in your carb, the idle air bleeds are the 4 outer ones in the top of the carb?

 

advancing the timing may help. you may be able to limit the total advance stop so it doesnt over advance but are able to have more advance at idle.

 

No, it isn't.
As mentioned, check the secondary throttle plate adjustment. The adjustment screw is usually accessable from the bottom but you can remove it and screw it in from the top so that in the future it can be adjusted without removing the carb. Some say to adjust the rear blades so that the idle slot opening looks like a square under the blades. In my own experience that can be too much but every engine combination can be different.

When that's right try the idle mixture screws again to get max manifold vacuum. With a single plane manifold they should be turned out pretty much evenly. With a dual plane just give the engine what it wants.

If it's still idling rich inrease the idle air bleeds. A little change can make a big difference.

 

Ok, I will try these ideas since they sound like "consensus".

And the "increase" the air bleeds was what I was wondering about in my original question. I don't know the carb theory well enough understand which way to go with them.

I agree, the carb is NOT too big for my engine. It runs awesome when I get above idle. I have run several 600 cfm carbs and never could get them rich enough under load, so I was forced to go to 750 to get it where my engine ran well.

But now that it RUNS well, it idles too rich.

 

as mentioned b4. bring up your idle speed. 600 is too low.

 

But it sounds so COOL! I love sitting at red lights with it idling just where the engine rocks the car with the lope.

 

What do you guys think, 800 rpms?

Doesn't it kick out of the idle circuit around 900?