Holley 4160 fuel puddling in Offenhauser 6116DP.

[lokutus78]

Hey guys. I have an principle question about the Offy 6116DP and a Holley 4160 390 CFM. Some engine specs:
Cologne 2.8L V6
Mild cam Kent V6T2, Duration 280°
Ported runners
Janspeed header
Higher compression
Flywheel lightened
Duraspark ignition
Holley 4160 390 CFM
#51 main jets
#59 secondary metering plate
#4.5 PV

Problem: Engine has rough idle, unequal fuel distribution, spark plug 3+6+1 more or less black, the rest grey/dark gray.
I had some test runs and tried a lot with adjustments and changed parts.
Primary system seems to be fine. react well to idle screws. (2 turns out.)
Engine starts very well, revs like hell, but idling is a nightmare.
At higher RPM you can hear how some sparks are missing through pulling in the puddle of fuel.
Transition slot fine, bowl level fine, all seals are new, no dripping booster, all holes and canals are free, secondaries plates completely closed.

It seems that the idle vaporization is too bad. I can let run engine for minutes constant with 3000 RPM and more and the puddles didn't disappear. How can this be? At the moment I've disabled the secondaries (bowl empty), because they are also flooding the upper section of the manifold, but in normal condition where should this fuel going with closed plates? Does anyone had similar problems or has some ideas for setup? Thank you in advance! Denis

[Gaz64]

Hi Denis. With your unequal distribution, the inlet manifold is more the cause. Especially if you have modified it in the plenum area, etc. All Holley four barrel carbs run a constant discharge idle circuit on the secondaries if two corner idle, as in your case with a 4160 390. This is to keep the fuel in the secondary bowl from going stale. Can you post some pics or video of what's going on here please? Gary

[lokutus78]

Hi Gary. Thank you for the answer. So far, I know that manifold is known for unequal distribution. I've only rounded some edges. If you have a "normal" manifold, then secondary idle discharges in same runners like primaries. So there is always a airflow. But at this Offenhauser dual port manifold there are two manifolds, one for primary and one for secondary. The point for me is: The fuel comes out of secondary idle system and there's no airflow (excepting heavy load). And so the fuel has no chance to taken away and stays at secondary manifold bottom. Next thing I have to do is give more initial ignition timing without.vacuum advance. Caused from other cam with longer duration the engine need this. Idle speed should rise up, maybe better for A/F ratio adjustment.

Question: I measured the primary idle discharge port near the plates, they're ~1.7 mm (1/16"). Compared with a Solex 35 EEIT it looks big for me. It is the factory size? What if I decrease the size of that hole to 1mm or so? I hope i get smaller droplets of fuel to give better vaporization. Anyone tested this? At picture, see that soaked seal. Is it normal? Denis

[Gaz64]

Denis, do you have the carb on backwards, since the primary is the bottom of the manifold. The primary side needs engine heat for vaporization, the secondary side is on the top side for power.
I'd cut out any part of gasket that does not match the top of the manifold. The primary side idle discharge ports in a Holley is not the restriction, the fuel and air jets are elsewhere in the carb.
The mixture screw controls the idle emulsion volume via the discharge port. It's a fuel/air mixture via this port, not liquid fuel only. Gary

[lokutus78]

Hi Gary. Yes I had the carb backwards; primarys to bottom to use the heat. Oddly enough are the primary runners bigger than secondaries. I tried it one time the other way, but wasn't better. I know that all fuel is emulsified before it reaches the manifold. This ratio is calibrated by Holley by IFR and air bleed size. Maybe there's something wrong inside the metering block? All holes are as I got the carb. Is there a possibility to measure the emulsification ratio? I'll try another gasket, matching only outside. The old one is worn. Denis

[Gaz64]

It seems that the idle vaporization is too bad.

Every dual port manifold photo I can find shows the primary on the bottom and feeds the small runner per cylinder.
This is absorb heat from the engine for vaporization, and to have high gas flow velocity to keep fuel in suspension.
The secondary runners are on top, "insulated" from engine heat by the primary runners, and have the larger runner size for power demand.

I can let run engine for minutes constant with 3000 RPM and more and the puddles didn't disappear. How can this be? At the moment I've disabled the secondaries (bowl empty), because they are also flooding the upper section of the manifold, but in normal condition where should this fuel going with closed plates? Does anyone had similar problems or has some ideas for setup? Thank you in advance! Denis

The manifold vacuum in both planes will be the same regardless of throttle opening. What's the list number of this carb? Gary

[lokutus78]

Attached a pic of that manifold. As you can see, the secondary runners are smaller than primaries, size not much more as a thumb. Offenhauser has tested this manifold for one year or so. I hope they knew what they've done. ;-) Yes, of course both planes see same vacuum, but the primary plates are used permanently and are opened a bit for idle. The secondary idle discharge ports are sucking from the (same) vacuum and get no air (plates closed) to take the fuel away. So it'll be more & more until there's a sea and runs down the runner. List number is 8007 (build 0373). Denis

[Gaz64]

I think you need to try a different carb on there. A 8007 is meant for a small V8. The recommended carb for a small V6 is a 6299. Your manifold as a two piece does not have the same dual port theory as other manifolds. Your bottom half is really a single-plane, divided 360 manifold. Gary

[lokutus78]

Question. It is normal condition that this chamber at secondary side (I know the photo shows primary side) is full of fuel after running engine? Denis

[Gaz64]

This is a 8007 which has a metering plate, not metering block on the secondary, correct? When you say "full of fuel", if it's completely liquid, and the power valve vacuum port is NOT drilled through from the throttle body like the primary side, then it's not a concern. Gary