426 Street Hemi Idle Problems

[67 WS23]

4.5 psi is a bit low, will give low fuel level; about 6 is better.

For now, 4.5 is fine. At first it was set at about 1 psi and the engine wouldn't idle. I winged it until it would idle, at about 2.5 psi, then at idle I set the regulator at about 4.5. I have no intention of driving the car aggressively, or even off my block until I get a better pump, probably an Edelbrock. 6 psi would be on the cusp of overwhelming the needle valves.

Currently I'm using a 1966 washer bottle with the hose bib as a fuel tank. Idling for about 8 minutes dropped the fuel level about a half inch. I need to calculate the fuel use after I figure out how much fuel that actually was. The engine idles well for not running for such a long time. But it's been parked in weather-tight garages since I've owned it, 40 years now, so I wasn't expecting any issues. I was sure to prepare it by hand-rotating the engine with fresh oil in the cylinders, cleaned and re-gapped plugs, cleaned points, etc. Still, it needs a complete tune up with new plugs, wires, and points. Those have all been in the car since I bought it in the 1980s.

I have a rust hole on the torsion bar support I need to fix before I run the new fuel line. I also haven't installed the new tank yet, I wanted to wait until the engine was running again. I figure by next spring I'll get the tank in and the car off the jack stands and finally out of the garage.

 

[Geoff 2]

No,
Carter & Edel carbs will accept 10 psi. 6psi is not on the cusp of anything.
Edel mentions a setting of 5.5 psi, because fuel pressure changes the fuel level & the E carbs are calibrated for 5.5 psi/7/16" float level as a datum point. A higher fuel level will result in a richer mixture, lower fuel level is leaner.

 

[Geoff 2]

Should have added this chart. Note the 10psi....

 

[Dragon Slayer]

It is also because EB uses the smaller style float which provides less buoyancy force against the needle. You also need to remember Carter MOPAR for the BB were predominately .1015 needles. Almost all the kits now a days come with .110 as standard and many are metered larger. If you look at the chart and let's say 6 psi, that means you need and additional 4/64" float drop (1/16") to compensate for the greater force the fuel pressure applies to the larger needle diameter.

 

[67 WS23]

Should have added this chart. Note the 10psi....

View attachment 1713352

Per the chart (thanks for including), with a .1015" seat and a float setting of 7/32" (per the 4327 spec) 4.5 psi looks fine. The chineseum pump is likely far exceeding 6 psi. I didn't need a chart to know it was flooding... the original pump never did any such thing. The regulator at 4.5 psi gives a smooth idle, good response on the pedal, and no flooding. Anyway, as I recall from 35 or 40 years ago, the Carter AFBs don't like pressure to much higher than about 5.5 psi depending on temperature. I don't intend on driving the engine hard, or even leaving the neighborhood. I understand the EB fuel pump spec'd out for the 67 440 has much better pressure control, so eventually I will probably replace the chineseum pump and regulator to return to near-stock.

 

[1STMP]

4619 4620s stock newly rebuilt with new gas tank lines and fuel pump. Fuel vapor seperator present.
Only running ethanol fuel. thanks for the help.

"Only running ethanol fuel."
Is your carb(s) o-ring seals,
diaphrams set up for alcohol?
Ethanol can also wreak havoc on
rubber fuel lines and fuel pumps
if they're not rated to resist corrosion
from alcohol. And, the older the rubber
stuff, the worse the effects.

 

[not so famous bob]

No,
Carter & Edel carbs will accept 10 psi. 6psi is not on the cusp of anything.
Edel mentions a setting of 5.5 psi, because fuel pressure changes the fuel level & the E carbs are calibrated for 5.5 psi/7/16" float level as a datum point. A higher fuel level will result in a richer mixture, lower fuel level is leaner.

B>S>

 

[Geoff 2]

Read the chart. It goes to 10 psi. Out of view is the recommendation to run 7.5-8.5 psi for performance applications.
The fuel pressure in my Motors Manual for the 426 max wedge is.....6-8 psi....& the same for the 426 Hemi. That info is supplied by the manufacturer.....

 

[Geoff 2]

And from Carter....

 

[Dragon Slayer]

This argument has been going on for a while and in different threads. Folks forget there are ORIGINAL OEM carters, then later competition series, then Weber, then Edlebrock. Non of them are the same. Float size changed, needle orifice changed, float levels changed. So did the recommended fuel pressure.

Original OEM Carter and AVS did have higher fuel pressure recommendations from MOPAR. Even in the 50s and 60s. The Carburetors could handle it. The lower the fuel pressure, the easier it is to vaporize in the pump, and lines from heat before it gets to the carburetor. Determine what ACTUAL carburetor you have, what float size, what needle size being used and then base fuel pressure on that and the OEM recommendation.

 

[67 WS23]

This argument has been going on for a while and in different threads. Folks forget there are ORIGINAL OEM carters, then later competition series, then Weber, then Edlebrock. Non of them are the same. Float size changed, needle orifice changed, float levels changed. So did the recommended fuel pressure.

Original OEM Carter and AVS did have higher fuel pressure recommendations from MOPAR. Even in the 50s and 60s. The Carburetors could handle it. The lower the fuel pressure, the easier it is to vaporize in the pump, and lines from heat before it gets to the carburetor. Determine what ACTUAL carburetor you have, what float size, what needle size being used and then base fuel pressure on that and the OEM recommendation.

And from Carter....

View attachment 1715315

The 1967 Carter 4327S cannot handle too much over 6 psi without encountering issues with flooding. My recent rebuild is to factory spec. When regulated to 4.5 to 5 psi there is no flooding. The 2023 Carter chineseum pump is discharging 9.5 psi. I will be removing it soon and replacing it with an EB which has 6 psi max output pressure. The Malpassi regulator has controlled the flooding, without question.

New problem, the chineseum pump is thumping, making a racket. Next weekend it's history. On other forums these seem to be a common theme with the chineseum pumps; too high output pressure and they are prone to thumping/knocking.

 

[Geoff 2]

I have some AFB 'small' floats' & they look to be the same size as Edel floats. If there is a difference, it would be minor.
AFB, AVS & TQ can withstand a lot of fuel pressure because of the tremendous leverage the looooong float gets on the n/seat. I have run 10 psi at the track on a TQ, zero problems. Leverage ratio is about the same on the AFB/AVS.

 

[Dragon Slayer]

Leverage is not the only factor. It is buoyance too. What can hold more load. A 20 foot 3ft wide barge or a 20 foot 6ft wide barge. Those smaller float and not as long and thinner then the early Carter AFB and AVS floats.

 

[not so famous bob]

And from Carter....

View attachment 1715315

I had 2 426 hemis , both with the stock carbs ,most of the time , we never had to run fuel pressure that hi ,and never tried it .
we did have to put an a.c. idle solinoid on the drag car to stop it from dieing after a burnout when I let off of it , but , that was with a jetted rat roaster intake ,which puddled gas back in the day , but worked very well for drag racing..

 

[67 WS23]

I have some AFB 'small' floats' & they look to be the same size as Edel floats. If there is a difference, it would be minor.
AFB, AVS & TQ can withstand a lot of fuel pressure because of the tremendous leverage the looooong float gets on the n/seat. I have run 10 psi at the track on a TQ, zero problems. Leverage ratio is about the same on the AFB/AVS.

Some of the newer chineseum Carter fuel pumps put out way too much pressure for stock mid- sixties Carter AFBs, in particular in my case, a dead stock recently rebuilt to factory specs Carter 4327s.somewhere around 9.5 psi. We're not the only one to have observed this. They must be used with a regulator to prevent flooding the carburetor. The chineseum pumps also thump and knock, another observation by many. Maybe not all pumps, but they should be given second thoughts before using them. In my case, it will be replaced by an EB unit spec'd for Chrysler big block applications, that has a max output of 6 psi. It costs more but it will return the engine bay to stock appearance.

 

[Geoff 2]

I do not believe the Edel floats are different to AFB floats. While it has been a while since I have handled an Edel float, from pics they seem to be the same as the small Carter floats.
Below are all Carter floats. The end shape is slightly different on a couple of them, most likely due to a different supplier rather than some operational difference.

 

[Dragon Slayer]

Orig carter for Mopar mostly used the float on top. That is larger than the floats below. Different AFB for other cars (Cad as example) used the smaller floats. Later Carter and EB used smaller floats also. The AVS floats were also different but similar. Mount end had different look.

The principle is Buoyancy, Center of Gravity of the float with the Leverage length. The submerged portion equals the force applied to the needle through the center of gravity.

The larger the float size can apply a larger force with less submergence. Hence a swap of floats would change the bowl level. The needle would close sooner and the level of fuel would be lower with a larger float, unless you make an adjustment for float height.

You can observe the level by pressuring a carburetor with the rear venturi out. Then look at the level in the pickup well.

 

[67 WS23]

By analysis, the theoretical maximum pressure the needle valve in a properly set-up Carter 4327S carburetor is approx 7.5psi. This ignores friction in the pivot pin and the mass of the needle itself. The needle area facing the pressure at shut-off is approx .089 in^2. At 7.5 psi this is approx .6675 lbs. The float/needle valve arrangement is a class 2 lever system. If the lever length is (a generous) 2.83" and the effort (buoyancy) force by the float is .065 lbs (using the float volume and the density of gasoline) the load position of the lever is calculated at approx .250" at 7.5 psi input pressure. Not coincidentally, the position of the needle is measured at .250" from the pivot on the actual float. More input pressure would require a change to the needle location along the lever to a lesser dimension than the measured .250". This, of course, is not possible as everything in that system is at a fixed location.

So again, 6 psi is at the cusp of overcoming the needle valve when including the other factors such as the needle mass (I did not include) and the friction of the pivot pin. The absolute maximum pressure is calculated at 7.5 psi. As I have mentioned earlier, the EB pump puts out a maximum pressure of 6 psi with is within the design capability of the needle valve arrangement in the Carter 4327S carburetor.

 

[67 WS23]

No,
Carter & Edel carbs will accept 10 psi. 6psi is not on the cusp of anything.
Edel mentions a setting of 5.5 psi, because fuel pressure changes the fuel level & the E carbs are calibrated for 5.5 psi/7/16" float level as a datum point. A higher fuel level will result in a richer mixture, lower fuel level is leaner.

Fuel pressure does not change the fuel level, and a higher fuel level does not change the mixture ratio, at least not on the Carter 4327S carburetor or any other carburetor I am familiar with (over the past 45 years). The fuel pressure determines the fuel flow rate in time through the fuel line and other orifices between the fuel pump and the fuel bowl. The "mixture" is the air/fuel ratio which has nothing to do with bowl level unless the bowl is starved for fuel. The mixture is a result of venturi flow volume and fuel metering.

 

[Dragon Slayer]

Not sure of your math. If the needle is #38 .1015" dia, the area is 3.1416 x .05075 or .1594 squared. The volume is only submerged volume. The lever calculation needs to know the center of gravity of the float. Granted you can make basic assumptions for generic calculation.

The Fuel pressure absolutely changes the fuel level and mixture ratio. The higher pressure goes, the more force holding the needle open. The level of fuel must rise more to get greater buoyant force to close the needle. Now fuel level is higher. High fuel level in the well means less pressure differential to draw fuel up the venturi tubes. Hence easier to get fuel, and carb goes rich. Vice versa if you lower fuel pressure.

For mechanical pumps, they are diaphragm. Constant volume per pump (ideal). Pressure does effect flow speed and also raise vapor pressure to prevent temp boiling of fuel, but not the volume per stroke. No once you get to high RPM all sorts of other factory come in and rate of flow is important. Hence why a mech pump doesn't have a linear flow rate and in fact can drop off at higher rpms despite stroke rate.