Carbed Fuel Delivery Issue

[tulowd]

Hey All:

Since I am now a year wiser, I thought I would ask for some help in rectifying the ongoing fuel delivery saga on my 333 carbed Fox vert. Car put down 388 hp at DaSilva; but was running at 14:1 AFR; so it was lean with some more power available. Locked out distributor, 37* timing; marks on plug electrode indicate perfect timing.

Full AN8 feed, return and vent setup; sumped OEM tank; Pro Systems 780 road race carb; ported Victor Jr Intake Mallory billet return regulator; Comp 140 Mallory pump

Pump started getting noisy once warmed up; even after I relocated it parallel to the sump output lines. Idle and fuel pressure appear to be stable, however the throttle response and cleanliness of the idle varies. Makes no difference if tank is empty or full or anything in between.

Burned out a Holley billet HP150 last year during the heatwave - Holley blamed the ethanol content; been only running Shell 91 since. Replaced the Comp pump yesterday with known good Edelbrock and same thing continues to happen:

Car has killer throttle response and power like a raped ape when engine runs the first 10 minutes.
AFR looks good, a little rich, meaning I need slightly smaller primary jetting; but it's good to dump fuel on a locked out distributor to keep it from pinging/ detonating.

Once warmed up, AFR goes full lean and only shows acceptable numbers while decelerating with no throttle. At highway speeds it sometimes does not even do that unless down a hill. Throttle response and power disappear. Plugs look great other than a couple have the soot ring around the outside, due to the overly large primary jets. Once it does this, no top end power and for sure a lack of fuel. Yesterday she definitely ran out of fuel on a 3rd gear 6000 rpm on ramp honk; so is it not getting the fuel volume or is the fuel aerated or is there more air going into the motor?

About to delete the return setup and try running the pump with out a regulator and then with my old Paxton deadhead reg.

Could it be:
fuel is simply being aerated from being dumped at the top of the tank thru the return line (no tube; simple splash down).
a vacuum leak (between the intake and heads or ?)
the carb is doing something goofy? Float levels etc are fine

Water temps always between 170-180 even on scorching days, other than when stuck in traffic.


Any suggestions or comments most appreciated - the difference in power and drivability is huge and I'm running out of patience.


Thx boys and girls

[TurboFox]

What does your fuel system look like between the regulator and the carb? Are you running a fuel log?

[tulowd]

-6An lines from regulator.




UPDATE: deleted regulator, now only running pump with adjustable pressure. It gets better when I run at 8 psi.

It appears the fuel bowls are very very hot, never noticed that before.

Makes sense, as the problem is most obvious in hot weather; the higher pressure compresses the air bubbles somewhat, and would explain the inconsistent AFR readings.

Gonna look for the phenolic spacer and a heat shield now. Then going to put the return regulator back on and see how it functions at the higher pressure. <Might even try the Comp pump back on too?

[Slope]

Do you have a pic handy of your fuel system near the carb?

I'd be hesitant to ditch the return-style system especially if fuel heating could be present.

What do you have for jetting/power valves?

[Stephen06GT]

If the fuel in the bowls is hot, is there a chance you are getting some form of vapour lock?

[tulowd]

Do you have a pic handy of your fuel system near the carb?

I'd be hesitant to ditch the return-style system especially if fuel heating could be present.

What do you have for jetting/power valves?

6.5 PV's front and rear; 78/80 jetting which is a little too rich, with proper fuel delivery; so likely back them down a little once this little dilemma is solved

[Slope]

Excellent shots. Everything on the top side appears to be out of harm's way.

I take it that your under car lines are isolated from exhaust heat?

Also: plug the power valve in the rear metering plate and re-tune.

[Ponyryd]

^Was gonna suggest the same thing about the exhaust, very common of efi applications.
What I'd do is put a sight glass in line just before the carb, then you can see if its being aerated once it warms up.
Also, the return fuel should be running down the side of the tank, not directly into the fuel. Guess it doesn't matter now that you changed it though.
I'd also be checking the temp of the pump when its acting up. Where is the pump in relation to the tank?

[tulowd]

Excellent shots. Everything on the top side appears to be out of harm's way.

I take it that your under car lines are isolated from exhaust heat?

Also: plug the power valve in the rear metering plate and re-tune.

The main problem is in the primary circuit, as it is noticeably rougher and inconsistent at 1/4 throttle or less. The problem seems to be fuel temp / aeration related. Likely the latent heat in the float bowls is making it worse when the return style system is in use, since the fuel already has a higher percentage of air in it once it makes it to the bowls. Then as it boils, because it contains more air, it becomes worse than the simple non regulator setup now. Running at 8 psi reduces the symptom, but does not address the root problem of temperature; which seems to be coming from the motor, not the pump or system.
Fuel lines are run far away (other side of the frame rails) from exhaust except near the tank; the return line was installed after this photo was taken.




Carb is setup almost perfectly, but it cant function when the fuel is inconsistent; both temperature wise and air content.

[tulowd]

^Was gonna suggest the same thing about the exhaust, very common of efi applications.
What I'd do is put a sight glass in line just before the carb, then you can see if its being aerated once it warms up.
Also, the return fuel should be running down the side of the tank, not directly into the fuel. Guess it doesn't matter now that you changed it though.
I'd also be checking the temp of the pump when its acting up. Where is the pump in relation to the tank?

The amount of heat in the bowls is amazing. The fuel lines are always cool near the regulator, leaving me to believe the heat is coming from the motor, not somewhere in the fuel path.



Edelbrock pump is mounted similar, except it has the big filter in front instead of after.