lean spot when coming into the secondaries

[Marx3]

Same car / engine / carb as in my other thread.
When driving around with my wideband hooked up, I noticed that the AFR goes rich as it should ( about 12.5:1 ) once I get into the secondaries, but leans out a bit ( about 13.5:1 ) for a second and then returns to a safer richer ratio.
I am running stock CP needles afair,. raised the hanger a bit to hit 12.5:1. but why do I get this moment of semi-lean afr, once the secondaries have opened?

Are the butterflies bouncing maybe?
It is not something that can be felt at all. just shows on the wideband. 13.5:1 is too lean for my liking in a 10:1 iron headed engine

[Cliff Ruggles]

You may be seeing the secondary POE wells being sucked low or dry......Cliff

[Marx3]

The holes are at .040 as always...
Would it be bad to go to .042 or so?

[Cliff Ruggles]

Not sure, I try to keep them smaller so they don't continue to add fuel and make things too rich.  There is no other reason to be seeing a momentary lean spot unless the bowl is going low for a second, then filling back up and recovering to the richer A/F ratio.

I'd certainly address fuel delivery before opening up the POE holes.....Cliff

[Marx3]

I can hold it at wot forever.  ( on an empty freeway for instance )
Don't think anything is wrong with the fuel delivery?
Once it goes wot and rpm climb, it tends to ping a bit, but only at "higher" rpm.

Wait, which holes are you referring to when you say poe... The ones in the bowl, the ones at the bottom end of the tubes or the hole up above the air flaps?

[Cliff Ruggles]

Secondary POE is the system that feeds fuel to the top of the airhorn and delivers it to the engine thru the holes just above the flaps.  Some models have the holes in line with the flaps, others have them under the flaps, but they all do the same thing.

The restriction to the wells control the fill time.  When the secondaries first come on line the quick vacuum differential above/below the flaps pull fuel from the POE system and help to eliminate a momentary lean condition.  The engine also gets some POE fuel from the main nozzles from what fuel is in the passages just under them......Cliff

[Marx3]

When you say "opening up the poe holes", which holes of the holes in the poe circuit are you referring to?
The one up by the flaps or the ones down in the bottom of the poe tubes?

[Cliff Ruggles]

The fill holes are for the wells, the discharge holes are in the airhorn.

The fills holes determine fill rate, discharge holes determine how quickly the fuel in the wells is delivered to the engine.....Cliff

[Marx3]

Gotcha. So in order to address a lean secondary spot, I make sure the fill-rate is proper (holes at .040 ) and then try and up the size of the discharge holes. ?

[Cliff Ruggles]

I would only open up the feed holes.  One change at a time is always best with these things......Cliff

[Marx3]

And which are the feed holes?
The fill holes or the discharge holes?
Or the holes at the bottom of the tubes?

[77cruiser]

I'd open the discharge holes a bit. Do you know what size they are now?

[Marx3]

Havent measured them.
As far as I remember, the carb is a late 70's pontiac unit, that would propably have come off a 400.
I'll get by the car and have them measured asap.

What size, should I be seeing?

[Marx3]

discharge holes measure in at about .052. 
The next size drill bit I have ( right now ) is a .058, so I didn't enlarge them yet...

[77cruiser]

What hanger are you using?