Weber Fuel Return Line

Neal

Lifetime Supporter
I want to install a return line for my webers as I have too much fuel at the carbs. I've put Holley 1-4 psi regulators on each pump set at 3 psi. Do I plump the return line directly to the tank or do I put a pressure regulator in the return line and use that to regulate flow?
 
The regulator goes between the fuel pump and the carbs.

Are you using a pump that was designed for carburetors or a fuel injection pump? A carb type pump shouldn't need a return line. Your problem may be the wrong kind of pump.
 

Neal

Lifetime Supporter
I'm using Carter P4600-HP pumps. These are rated at 100GPH @ 6-8psi. Similar to a Holley Red pump. Definitely for carbs...
 

Lynn Larsen

Lynn Larsen
So the fuel goes from the tanks to the pumps. The outlets from the pumps both have regulators on them. Do you then go through a selector valve or do you have check valves on each line? Either way, the return lines should then go to the tank that is being pumped from. This is why I used 4 to 2 selector valve in my EFI system where a return is the norm. When I select the tank to pump from, I am also selecting the tank to return to. Jag messed this up at one point and if the return tank was full, gas would run out the vent onto the ground. Not a good thing everyone would agree.

I am assuming this setup allows high flow rates to the carbs for WOT/high load situations without the needle valves being subjected to too much pressure during idle and partial throttle situations. Would a single regulator nearer the carbs work or are you protecting the selector valve also? I would need to see a diagram of you fuel supply system to say any more.

Regards,
Lynn
 
Neil,

I think we're mixing our paradigms here. Forgive me if I've missed something but here's my take on this.

Carb systems need 2-8 psi. Nice systems have a low pressure fuel pump and a pressure regulator between the carbs and the fuel pump. The fuel pump has a bypass circuit for when the fuel system is full and up to pressure. Fuel is pumped to the carbs where the fuel bowl is filled and fuel is metered into the airstream. The level of fuel in the bowl is critical and controlled by the float valve. But you know all this because it's the system you have.

EFI systems require about 50 psi. It requires a high pressure fuel pump that has no bypass and will burn out in a short time if it runs dry. Most EFI pumps are submerged in the tank. GT40 tanks with their long and thin profile would be prone to allowing the pumps to run dry due to acceleration and braking with partially filled tanks. The filtered fuel is fed to the high pressure pump and then run through another filter and then on to the fuel rails which feed the injectors. Downstream of the rails is the bypass regulator. EFI systems have need to circulate fuel through the rails and have the bypass regulator downstream so no air gets trapped in the rails which could run some injectors dry.

So how did you reach the determination the carbs are getting too much fuel? What are you seeing to make you say this? Black smoke?

The carbs should easily handle 3 psi and the fuel pump will bypass once the flow slows down.

Bypassing the fuel back to the tanks requires a special valve (as stated previously) and you don't need to get into a complex system to do something that won't fix the problem, IMHO. If I'm missing something let me know. Please feel free to call me on the Xtreme line at 540-592-3030 if you want to talk about this.

Mark
 

Neal

Lifetime Supporter
I think we are on the same page. My current system is setup with one pump, filter, and pressure regulator and pressure gauge per tank. The two systems are joined to a solenoid valve that allows me to select right or left tank and pump. The valve has provision for a return line much like an EFI setup. All plumbing is AN -6.

The reason I bring the issue up is the motor is running quite rich. Black smoke, some reversion into the carbs, and a noticeable smell of gas. The motor was dyno tuned and ran perfectly. No changes have been made to the setup since the motor was dynoed. The plugs are consistently carboned indicating a rich condition.

I actually have the return line in place, unconnected. I'm curious if anyone running webers has needed to go this route. I'll check for a stuck float or needle.
 

Ron Earp

Admin
Hi Neal, I'll pull the carbs and check the float heights. You should not need a return line, there are 100s if not 1000s of Cobras and other that do this with no return.
 
[ QUOTE ]
The motor was dyno tuned and ran perfectly.

[/ QUOTE ]

Could you have the wrong idle jets? You were probably only running on the main jets when it ran on the dyno.

On my car (a CAV), I have the standard dual pumps going to individual pressure regulators & anti-backflow valves. Then the outputs go through a tee and on to a second pressure regulator at the carbs (it came with the carb setup from Inglese). The CAV-supplied regulators are set to a higher pressure than the Inglese one. Somewhere along the line (I think when my engine was dynoed), the diaphram in the Inglese regulator ruptured (I'm guessing they fed it from an FI pump and blew it out) leading to some nasty over-rich conditions. When I noticed raw gas spewing out of the Inglese regulator I knew where the problem was /ubbthreads/images/graemlins/shocked.gif. Anyway, the carbs saw well over the 2.5 or 3 PSI that they wanted, and the plugs were all fouled. One was wet with gasoline. After replacing the regulator and cleaning the plugs, it ran a whole lot better, but still rich. And this was at sea level while it's jetted for high altitude so should have been running lean. In any case, most of my driving was at part throttle so was on the idle jets. Now the weird thing is that I'm told my idle jets are too lean (as indicated by having to back out the idle screws 2 1/2 turns) and that this is what is causing the rich condition. Sounds strange. My car hasn't been touched since August, so I don't have a resolution to my problem yet, but in any case it seems to be the idle jets.

According to Mickey Lauria:
[ QUOTE ]
On a correctly-jetted idle circuit, the mixture screw on a 48 IDA is never more than 3/4 of a turn out. This will hold true 100% of the time, no matter what anyone else tells you. If you have to go more than that, you'd better heavy-up the idle jet.

[/ QUOTE ]
My Webers are IDFs, but still 2 1/2 turns is too much...

So... How far do you have to back out your idle screws?
 

Jim Rosenthal

Supporter
Maybe try Pierce Manifolds....I have never heard of a carb system where fuel flows BACK from the engine to the tanks. The fuel pump should have an internal bypass that opens when the line pressure rises,ie when the float bowls are full.
 
Some aftermarket pumps are positive displacement like the EFI pumps (Aeromotive for example), and when used in carb or EFI use you must use a return line. It really depends on the design of your pumps. Also some carbs do not like excessive pressure, and the needle valve does not shut, etc.
 
Hey Neal,

I guess my explanations get a bit convoluted sometimes. I just didn't want to come out and say returns are for EFI and not for carbs but that's what it comes down to.

Sounds like you have tuning issues. Is there a Weber tuning expert anywhere near you? Alternatively you can buy a Weber tuning book and dozens of jets and a maybe a few emulsion tubes and do it yourself.

You need to get a lambda meter on it and find out how rich it is in which different RPM ranges. Then figure out which jets to tweak, tweak them and test again. If it's rich throughout the range drop the main jet size. If it's OK or a little rich at speed but smokes a lot at idle there is an idling jet that's not to be confused with the idle mixture jet.

Haynes has a good book for Weber parts and how each model works. Jetting is more of an art and I have not seen a book on jetting Webers. Webers can be a bear to get right but once they're right they wail.

So back to my first question: Is there a Weber tuning expert anywhere near you?
 

Howard Jones

Supporter
1. The engine ran fine on dyno.
2. Car sat for some time without use.
3. Now carb(s) running very rich.

Conclusion; One or more of the needle and seats are either obstructed or stuck. This happens all the time. Also new fuel systems with a lot of plumming like the ones on our cars, and even more so on yours, tend to shake all the little pieces of crap loose soon after you start running the car. If you used assembly lube to build the stainless hose fittings, used too much and some of it remained in the lines, it gets hard after a while and breaks up into many small pieces of crap. Anyway the litle piece of crap is now lodged in a seat or some other important spot in one of the carbs. This seams to be one of those murphy's law things.


Fix; Take it apart and find the little piece of crap. You might be able to narrow the bad carb down by looking at the sparkplugs.

Happy New Year
 
That's what I get for speed reading a post. I didn't catch the car just came out of storage.

1. Evaporating gas from an unused carb leaves a residue. This residue can eventually cause the moving parts to stick. It's best to run the carbs dry before storage.

2. Gas has a shelf life. I've found it lasts longer in a dry environment (unlike Seattle). Try something like Stabil for storage or drain the fuel and refill with fresh gas in the spring.

If you have old gas, drain it from the tanks and carbs and refil with fresh. While the carbs are apart clean up all internal parts with carb cleaner. Pay particular attention to the emulsion tubes. That's where air is mixed with the gas. If that's not working well she'll run rich.

Try to run the carbs dry before you store the car. This reduces the amount of gum and sediment left from evaporating gas.

Sounds like you could use a good cleaning and fresh gas. (and no rejetting, sorry)

Mark
 

Neal

Lifetime Supporter
Well I did a little sluth work. Popped the carbs opened and found excessive fuel in the last in the feed line. Too much pressure. Check the pressure gauge against another and found the gauge to be off my 3 psi. Cranked the pressure down and things calmed down. I did install the return line and that helped more. Throttle response is crisp, idle good. Shouldn't have trusted the FP gauge. Unfortunately I found a small exhaust leak at the #7 flange. New gasket time...
 
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