[Tarl]

Hi All,

Having an issue with 66 lemans with a 1970 455 (462), SD Performance prepped #96 heads, Stump Puller Cam (Comp Cams 230/236 112), HEI, edelbrock peformer intake, Holley 4160, RA manifolds and pypes 2.5 x-pipe exhaust, AC Delco R45S plugs

It's running rich I think, all 8 plugs were carbon fouled and I see carbon buildup on the pistons after 5K miles. I just started it up after being in an auto cocoon for 3 years.

I cleaned the plugs and regapped them at .45, for some reason they were much less with #3 plug actually touching the electrode, don't know why, can't remember if I effed it up quite a few years ago.

It does seem to be idling much better, still runs with a bit of a lope, about 750rpm at 12 degrees BTC, but it's still running rich I think. I don't have a fuel pressure regulator but the gauge is 7psi at idle.

The Holley is dual feed but only has the front mixture screws, those are only out 1/2 turn, rear float was ok, front float I lowered 1 full turn.

Tail pipes seems to have excessive smoke and moisture (will try to attach video) and my eyes tear up after 2 minutes of idling.

So I can't figure out why its running rich. My shop is next town over so there would be a delay in me getting out there to try stuff.

Here is the video.

https://youtube.com/shorts/0qrVQ5xFC9s

[JLMounce]

Do you have the vacuum advance installed and adjusted? 12BTDC sounds about right, but you need another 10-12 degrees in vacuum advance at idle and cruise on top of the mechanical advance. That may be part of why it's running rich. At low load you need the extra lead to burn all the fuel mixture.

at 7psi, your fuel pressure is probably okay, but if you can drop it a pound, that may also help.

[Tarl]

It's hooked up, I will double check what the actual advance is.

[Kenth]

Adding vacuum advance at idle makes stronger vacuum signal in intake and atmospheric pressure will push more fuel thru the idle circuit.

I would look for dried up, stiffened, power valves not closing at the proper vacuum value stamped on them.

HTH

[Tarl]

Was just reading the manual for the 4160,, I was setting the float level with the engine off, but the manual says idling. so the float level may still be too high.

[steve25]

Something is way wrong if your motor when warm idles best with the mixture screws 1/2 turn out!

[242177P]

Originally Posted by steve25

Something is way wrong if your motor when warm idles best with the mixture screws 1/2 turn out!

$5 says it's running extremely lean, not rich. Note
that he mentioned his eyes tearing up. Richen it
up, seriously.

[Tarl]

Originally Posted by 242177P

$5 says it's running extremely lean, not rich. Note
that he mentioned his eyes tearing up. Richen it
up, seriously.

Always thought it was due to excessive unburned gas that causes tearing up. Will pull them out another full turn and see what happens.

[Gary H]

If you have the mixture screws are out only 1/2 turn each, I will bet you have the throttle blades too far open, trying to get it to idle. Turn the screws out to 2 turns and see if the idle picks up. Set you idle RPM at around 850 with the idle adjustment screw on the drivers side of the carb. Then adjust the mixture screws to get the highest rpm. Adjust idle Rpm to 850 again. Also, put a fresh set of plugs in. I have had very mixed results trying to reuse carboned up plugs.

[tooski]

I had the same problem with my 750 DP 2 corner mixture screw carb. Eyes n nose stinging n watering. Idle AFR said low to mid 10's at idle. Plugs carbon fouled. Found the transfer slots better than 50% open, mixture screws unresponsive. Adjusted that , adjusted IFR's and IAB's and needed to add a bunch of idle bypass air. Mixture screws became responsive. Used the secondaries to tweak the idle speed. Idle AFR ended up in the high 13's, occasionally into low 14's. Exhaust still smelled a bit though.

[ta man]

https://www.holley.com/blog/post/her...ure_and_speed/

Take it step by step. First set your floats, make sure you have no vacuum leaks. Don't try and idle this engine at 750 shoot for 850 or so..its a healthy cam and needs a bit of idle speed. You have a lot of potential with your engine build keep plugging away.

[chiphead]

Was the carb rebuilt after the 3 year nap? Lots of seals, seats and gaskets can go bad in a carb once it dries out and sits. Likely it needs a rebuild and full re-baseline.

Running pig rich is the choke or the idle circuit. A 2 corner carb should have the idle mixture screws out 1 to 2 turns. Did the carb ever run well on this engine?

I've got a thread on here for tuning a 4150 double pumper. The primary side is about the same as your 4160.

[Tarl]

Carb has always run like it has, all the carbon fouling and buildup happened over the last decade. Electric choke seems to work fine and release properly. After cleaning and regapping its running better than it has recently, still a bit crappy.

Going to hit it Wednesday night with all these suggestions. Appreciate all the help!

[Kenth]

I'm surprised more people aren't bringing up the issue of old dried out power valves in Holley carburetors.
Of all the Holley/Autolite carburetors I've helped people with, these are the single biggest problem with high consumption, nozzle drip, smelly exhaust and soot black venturis.

[Formulas]

Another consideration after a 3 year cocoon Fuel quality.

Basically 2 ways to set holley floats not running bowl off physical measurements
or engine running bowl screws out watching fuel exit the bowl

the second way is most accurate as it takes in account fuel density float buoyancy, engine rocking, fuel pressure, carb tilt a dynamic event vrs static

also agree with a lean mix running you out of garage or throttle blades open to far to compenstate for lean idle resulting in nozzle drip the drip doesn't atomize as well at low rpm and stinks

[chiphead]

I agree, any carb that sits should have a full rebuild.

But if he says its always run like this, it's a tuning issue. The Idle Feed Restriction and the Idle Air bleeds controls the fuel mixture below 2500 RPM. A Holley main circuit doesn't deliver fuel from the boosters until the engine is well into cruise speed. Thats what I didn't realize when I started tuning my 750 DP. Most guys start reducing the size of the main jets, and it's the wrong thing to adjust. The idle feed restriction (IFR) is a smaller jet located in the metering block, that controls the amount of fuel delivered to the transition slots and the idle mixture screws. The transitions are at/above the throttle plates, and the mixture screws feed discharge ports below the throttle plates.

The primary transition slot opening at idle is the absolutely most important thing in a Holley. It gets overlooked, but I now understand it sets the table for the whole fuel map. You want about .015-.030" of the slot showing when the primary blades are on the curb idle screw. At idle, the transition slot bleeds air and fuel around the throttle blades.

As the blades are opened, the transition slot is more exposed. The high speed air around the blades pulls fuel from the slots. The fuel starts to come out of the transition slot more and the idle screw discharge ports less. At 1400-2000 RPM, 90% of the fuel the engine gets is coming from the transition slots. As you open the throttle more, the transition slot gets fully exposed. At that point, the fuel from the transition slot tapers off, and the main boosters start to deliver fuel.

So if you have the transition slot too exposed at idle, you'll get way too much fuel. Then as you accelerate from a stop, you run out of transition slot before the mains come on, so you get a lean spot or a bog or a hesitation. The accel pump can't cover that lean hole up, so the carb runs inconsistent. Rich at idle, and then maybe lean as it transitions to the boosters. Idle screws don't fix it, main jets don't fix it, accel pump doesn't fix it, lots of guys chase their tail.

Since the transition slot is fed from above the idle screws, the screws dont have any affect on fuel available at the slots. The idle mixture screws also become less effective, since the vacuum at the screw discharge ports has started to taper off, in favor of the transition slots.

The correct way to fix this is to close the primary throttle plates until you get about .020" of the slot showing. Then open the idle mixture screws about 2 turns each. There is a small screw underneath the baseplate that lets you adjust secondary idle. Back the screw off and then turn it in, until it just contacts the secondary arm. Then add 1/2 to 5/8 of a turn more, to open the secondary plates just a bit. Stock spec is 1/2 turn.

Fire the engine up and warm to operating temp. Set floats, choke, etc. Get engine to curb idle. Set the idle mixture screws for maximum manifold vacuum. Turn them in 1/8 turn at a time and look for stable vacuum. When the vacuum drops off, you can open the screws 1/8 of a turn and confirm the vacuum comes back up.

If it doesn't want to idle, you can add 2-3 degrees of base timing, that will increase the manifold vacuum and help things. You can also open the primary throttle screw no more than about 1/4 turn, otherwise you'll be exposing too much of the slot. You can also add an additional 1/8 turn to the secondary screw. The secondary screw is very touchy. If it idles too fast, you can reduce the primary/secondary idle speed screws a touch. The trick is to balance the front and rear barrels without either exposing too much/too little primary slot, or opening/closing the secondaries too much. Once it will idle pretty well, then you can set the accel pump so it doesn't hesitate on quick throttle movements.

If it still runs too rich (or too lean) after balancing the transition slot and adjusting the idle mixture screws, that's when you need to go into the primary metering block and look at the sizing of the IFRs to see what is going on. An AFR gauge is really helpful, as I learned. Sometimes what you think the carb is doing, and what its actually doing are very different, and the AFR gauge keeps you sane.

What is the carb list number anyways?