426 Street Hemi Idle Problems

[67 WS23]

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.

The needle facing the pressure is a cone.

 

[Orig69]

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.

View attachment 1716521

This is a float for a Carter AFB Competition series carburetor.

 

[67 WS23]

That's different from a stock float for the 4327S AFB. The fuel system as designed in the 1960s for the 1967 440HP, even using the stock 5/16 fuel line, is no problem at all. In fact it was wildly successful for the R/T and the GTX. The original owner of my car, who I purchased the car from, drove it 90k miles over a period of 15 years. However, for the umpteenth time, the stock 4327S cannot tolerate more than about 7.5 psi without flooding. My earlier calculation supports this. At 6 psi, due to needle mass and pivot friction, it's iffy. At my current regulated 4.5 psi, no flooding and the engine is more than happy.

 

[Dragon Slayer]

The needle facing the pressure is a cone.

And a hemi piston has a dome. The horizontal surface area is still based on the diameter of the bore.

 

[Geoff 2]

WS23,
You obviously have much to learn about carburetion:
- fuel level DOES change the A/F mixture. As D. Vizard explains below for a Holley, but similar for a Carter/Edel.
- venturi carbs have a spill height; it is the difference between the fuel level in the bowl & the highest point of the booster passage that the fuel needs to reach, which is usually the entrance to the booster. The SH is usually between 1/4 -3/8". Something has to physically lift the fuel to get into the booster. Venturi depression does that & if the distance to be lifted becomes greater, more depression [ vacuum ] is needed & therefore engine rpm [ airflow ] will need to be increased. Lower fuel level leans the mixture.
- n/seat size has an affect on fuel level AND how much pressure the n/seat will tolerate before flooding occurs. AFBs etc will tolerate 10 psi [ maybe a little more ]. The float size/weight of the TQ is nearly identical to the small AFB floats; plus the leverage ratio of both is near if not identical. I have run 10 psi with 0.111" n/seats, zero problems.
- the factory rated fuel pressure for the Hemi & 426 Max engines was 6-8 psi, & those probably had large n/seats to feed 425 hp.

 

[Geoff 2]

Should have added this....

 

[67 WS23]

WS23,
You obviously have much to learn about carburetion:
- fuel level DOES change the A/F mixture. As D. Vizard explains below for a Holley, but similar for a Carter/Edel.
- venturi carbs have a spill height; it is the difference between the fuel level in the bowl & the highest point of the booster passage that the fuel needs to reach, which is usually the entrance to the booster. The SH is usually between 1/4 -3/8". Something has to physically lift the fuel to get into the booster. Venturi depression does that & if the distance to be lifted becomes greater, more depression [ vacuum ] is needed & therefore engine rpm [ airflow ] will need to be increased. Lower fuel level leans the mixture.
- n/seat size has an affect on fuel level AND how much pressure the n/seat will tolerate before flooding occurs. AFBs etc will tolerate 10 psi [ maybe a little more ]. The float size/weight of the TQ is nearly identical to the small AFB floats; plus the leverage ratio of both is near if not identical. I have run 10 psi with 0.111" n/seats, zero problems.
- the factory rated fuel pressure for the Hemi & 426 Max engines was 6-8 psi, & those probably had large n/seats to feed 425 hp.

Float level, if too low meaning too little fuel in the bowl, will eventually cause the mixture to lean out. Atmospheric pressure mediated by engine vacuum draws the fuel. Metering or choke can lean or richen the mixture (We know this). The flooding in my case was caused by too high fuel pump pressure caused by the chineseum Carter pump. Regulating the presure down (to 4.5 psi in my case) solved the problem. I prefer NOT to have fuel all over the top of the intake, and also prefer the engine to idle. Therefore, I lowered the pressure to the needle valves.

 

[not so famous bob]

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.

you think a float that is overpowered by too much pressure , wont flood a carb and make it run rich as hell ??

 

[67 WS23]

you think a float that is overpowered by too much pressure , wont flood a carb and make it run rich as hell ??

I do very much. That's why I used a regulator to stop the flooding caused by the chineseum Carter pump. Regulating to about 4.5 psi did the trick.

 

[67 WS23]

I just put my rebuilt carb on my 67 R/T. I ran the car a few minutes at a time by filling the bowls with a small squeeze bottle, no problem. Then I plumbed in the new Carter fuel pump and I have massive flooding. The car will run for about 5 seconds, then I can see fuel all over the top of the manifold. I removed the carb and lowered the float levels, still no good. After a little research, guys have had similar problems with the chineseum Carter pumps. Too much pressure for the needle valves to handle. So I ordered a Malpassi in-line regulator to lower the pressure to about 5 psi. The regulator should come next week. I will update with the results.

Update

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.

Update: I ditched the chineseum Carter pump, regulator and pressure gauge and put in the EB pump. Engine operates perfectly with no flooding. I timed the engine back to 12 BTDC, adjusted the carb, and it idles smoothly at 750 rpm. Not bad for sitting idle for basically 27 years (one start in 2006 since 1997, totally idle since 06 - yes, new oil, cleaned/gapped plugs, manually turned the engine with a squirt in the cylinders while observing valve train, bore scoped the cylinders to look for anything I don't like, rebuilt carb, etc.). Next, refresh the cooling system and then off the jack stands.