Racing Fuel Systems

Hi, I would like to request some advice about resolving a carb issue. This main body is the classic style HP 4150. 1.475" venturis, 1.75" original Holley throttle plate. Bowls and hardware to match. It was running good on a BBC until the BLP blocks and transfer slot restrictions came into play. There have been no other changes. Below is a list of what was installed and attempted.

*BLP five emulsion adjustable blocks .026" kill bleed, top and 3rd emulsions are .028". All other emulsions are plugged.
* BLP supplied, red gaskets.
*.250" brass well plugs seated to stops just above the angle channels.
*The idle well, top, set screw plugs were installed by BLP.
* Stepped downleg boosters.
*.033" IFR in lower position. Upper position is open.
*.070" IAB primary and secondary.
*.028" MAB primary and secondary.
*.082" transfer slot restrictions - all four, set even with the main body, metering block gasket sealing surface.
*.062" PVCRs with 6.5 power valve in primary. Secondary PV is plugged. Each sealed to block with BLP O-rings.
*Power valve tests good.
*74 primary jets / 84 secondary. 74 primary was okay previously with .067" PVCRs but no wideband data. Wanted to try lower PVCR this time and use a wideband.
*32 / 35 discharge nozzles. Also tried 35 / 35 due to a pop back / hesitation which the power valve survived.
*Started out with pink cams in primary #2 position and secondary #1 position.
*30cc pumps.
*Squared primary transfer slots .020" - .026" - approximately 1.5 turns from initial contact.
*Tried rear transfer slots covered and squared = no improvement.
*Floats precisely at the bottom of holes and at the level of the top emulsion jets.
*Idle mixture screw settings tested are 1 turn, 1.25 turns, 1.5 turns and 2 turns out on all four corners. Any setting except 1.5 turns starts to shut the engine down worse.
*Timing was moved around to no avail. The richness was so bad all efforts seem to be a lost cause.
*Tried vacuum advance connected and disconnected - used manifold vacuum.
*No vacuum leaks.
* No fuel dripping from the boosters or being pulled from boosters at idle.
* Covering the IABs with my fingers on either the primary or secondary clears it up some and raises the engine RPM.
* The only thing I have come up with is possible leakage past the power valve O-rings, but they are not damaged.

Thanks!

Tell us a little about the motor and camshaft specs including LSA

Change the IFR to a 31 and the idle air bleed to 76, this is a big swing, adjust after this first move.

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I agree take a big swing at it and go down on ifr .031 / bleeds.you will know your close when idle mix at 1 turn to 1 1/4
And work up you coud go a bit smaller onthe tsr maybe .077
You say rich ? Are you using an AFR guage ? If not sooty plugs can be from big overlap cam at iidle
or lean misfire
How much idle vacuum
I have similar tune i. My BLP BLOCLKS .033/70 idles lean 13.8 475 bbc 250@.050 cam

How much initial timing

Adjusting the T-slot position at idle will change idle rpm. So when you set the T slot at 020, did the idle rpm increase or decrease from where it was?
A rowdy cam will normally require a higher rpm to stay idling. And it may not have enough vacuum to pull in the PCV pintle; this would allow a lot of air in at idle, requiring richer idle screw setting.
What is:
- idle timing
- min idle rpm that engine is comfortable with.

Also what heat range are the plugs

Thanks for the suggestions. When I said rich, I meant extreme raw fuel rich. The kind that wets spark plugs. I hope to have some stable vacuum and timing info tomorrow after work. It didn't take long to decide something serious was going on and it was time to shut down and abort testing. I went through the carb today and found a possible issue, but I want to make sure before moving on to different feeds and bleeds.

The issue appears to be caused by the O-ring seal and an older style power valve plug that has less sealing surface than more current ones. The O-ring is borderline close to the outer edge on new, Holley power valves as it is. I believe the rounded edge and narrow surface on this plug is letting fuel by the O-ring. I plugged the PVCRs in that block and installed a PV plug. I also installed a 4.5 PV in the primary to make sure it stays closed until I can get some vacuum readings. I realize it is not a big change, but LSAB were changed to .072" as well. IFR stayed at .033". If the issue persists, I'll move on to the feeds and bleeds. I'll get the heat range of the plugs as well. A new set is in order anyway. Which spark plugs would you recommend for this NA engine? I assume stock heat range but anything more specific?

The carb was brought to me, so I didn't get the chance to get much info before-hand. Vacuum and timing were unknown by the owner. The way it was running, I would have only been able to get nearly total timing anyway. As for RPM, the engine would not idle. It had to be held around 2,500 RPM just to stay running.

AC Delco R44XL or equivalent. R44XLS would be the extended tip plug.

This sounds like a wrong-gasket thing or plug-left-out-somewhere thing not a fine tuning issue to be fixed with different IFRs or air bleeds.