Need Help Carb Gurus

[Norwoodx55]

Long post, I will explain what I am working with before I ask my question.

I have an 1850 Holley that I put a 3310 primary metering block, a 4777 secondary metering block (no power valve or idle screw provisions) and center hung float bowls on. This carb is on a mild 355 with 9.25 CR and a Comp Extreme 262 cam that pulls about 14" of vacuum.

OK, bottom line is, even with the idle mixture screws all the way seated, the engine continues to idle fine. I have verified that I am not working with the reverse style idle screws. My first thought was that the power valve must be blown and is pulling fuel through the PV vacuum port in the base plate. The PV checked out OK, but I replaced it anyway. There was no sign of fuel being in the vacuum well either.

The float levels checked out and the needles don't appear to be sticking. Can't see any droplets or mist being pulled out of the boosters at all. The only place I can think of that fuel could be feeding the engine from are the transfer slots. The fronts are barely exposed by approx. the width of the slot, and the secondaries are fully covered.

Any ideas on where the fuel is coming from to keep the engine idling. The idle mixture screws are basically innefective. I have heard that in some situations that the carb may being "pulling over." I don't know exactly what that means but I imagine that the engine demand is pulling fuel over from the next circuit, either the transfer slots or through the boosters. I am hoping someone here can give me some insight to this problem.

Brett

[Shaker455]

Brett,
The Ide Feed Restriction (IFR) in the metering blocks may be too large espically in the rear block and as you said it has no screw to control the flow.

Measure them, they are the brass pieces on either side of the PV.
Jeff

[Norwoodx55]

Jeff, you da man!

The secondary IFR measured a whopping .110"!... I am using a metering block that I had previously drilled and tapped the IFR. I forgot to install a jet into the hole. It is now .033" and everything is working as it should. I actually didn't think the IFR would have an effect without the mix screw passages opened and in use. I was wrong, maybe it supplies the transfer slot too? Anyway, thanks, you made me look and learn something in the process. I have a lot to learn as an aspiring (rookie) carb tweeker.

While I have you here, I have another question. I have read that the right combination of IFR size and air bleed will net around 1.5 turns out on the idle screw. Is that for 2 corner idle carbs only, or does it apply for 4 corner too? Reason I ask is that on my Camaro with 4 corner idle, all my combinations have netted around 3/4 turns out.

[Shaker455]

Hey Brett,
I was going to say a .110" hole means it's wide open...so now you know it contributes!...LOL

Yes for 2-corner about 1.5 turns is good but nothing is written in stone.

If your 3/4 turns on your Camaro that's okay but your IFR may be a bit big or sloghtly over jetted....sometimes you see that....not a big deal.

[Norwoodx55]

Thanks, I appreciate the help and information.