fuel return line (carb)
01-01-04, 10:56 PM
#1
smog nazi destroyer
Thread Starter
fuel return line (carb)
i was looking through some pictures of similar setups (using weber ida's) and noticed that alot of them look like they have return fuel lines. should i be doing the same? how much difference does it make, if any?
(my goal here is to get more than 8 mpg around town and 12 on freways)
(my goal here is to get more than 8 mpg around town and 12 on freways)
Last edited by riffraff; 01-01-04 at 10:59 PM.
01-01-04, 11:16 PM
#3
smog nazi destroyer
Thread Starter
right now all that i have is the line taking fuel to my carb. (thus probably the problem).
i am running the standard holley pressure regulator that most of the people here use.
i am running the standard holley pressure regulator that most of the people here use.
01-02-04, 12:10 AM
#4
84SE-EGI helpy-helperton
You will need a return line, otherwise your float bowls are going to overflow and the engine will run rich at anything other than WOT.
Most carb setups - with the exception of what Hornbm is talking about - require that the fuel pressure pump provide a fixed pressure (usually 4-8psi based on carb throat size and bowl size), and this pressure is maintained by the needle valves and seats to set the fuel level in the bowls. Once the bowls are full, any overflow fuel is sent back to the tank via the return line.
If you aren't using a return style regulator, then the fuel pressure will overpower the needle valves and seats and allow the float bowls to fill up completely until they overflow - oftentimes sending this excess fuel right down the intake. This is why you're not seeing any fuel leaks, and also why you're getting such crappy mileage.
The return line should still be in place on your car, you'll just need to run some fuel line from the carb overflow outlet to the return line on the chassis. Good luck, and report back,
Most carb setups - with the exception of what Hornbm is talking about - require that the fuel pressure pump provide a fixed pressure (usually 4-8psi based on carb throat size and bowl size), and this pressure is maintained by the needle valves and seats to set the fuel level in the bowls. Once the bowls are full, any overflow fuel is sent back to the tank via the return line.
If you aren't using a return style regulator, then the fuel pressure will overpower the needle valves and seats and allow the float bowls to fill up completely until they overflow - oftentimes sending this excess fuel right down the intake. This is why you're not seeing any fuel leaks, and also why you're getting such crappy mileage.
The return line should still be in place on your car, you'll just need to run some fuel line from the carb overflow outlet to the return line on the chassis. Good luck, and report back,
01-02-04, 12:19 AM
#5
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hmm, I was curious about the same thing, except I have a 45 DCOE. Where would the fuel line run from on the carb? I don't see any place for a return line to connect to on the carb
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01-02-04, 01:10 PM
#9
smog nazi destroyer
Thread Starter
Originally posted by LongDuck
You will need a return line, otherwise your float bowls are going to overflow and the engine will run rich at anything other than WOT.
Most carb setups - with the exception of what Hornbm is talking about - require that the fuel pressure pump provide a fixed pressure (usually 4-8psi based on carb throat size and bowl size), and this pressure is maintained by the needle valves and seats to set the fuel level in the bowls. Once the bowls are full, any overflow fuel is sent back to the tank via the return line.
If you aren't using a return style regulator, then the fuel pressure will overpower the needle valves and seats and allow the float bowls to fill up completely until they overflow - oftentimes sending this excess fuel right down the intake. This is why you're not seeing any fuel leaks, and also why you're getting such crappy mileage.
The return line should still be in place on your car, you'll just need to run some fuel line from the carb overflow outlet to the return line on the chassis. Good luck, and report back,
You will need a return line, otherwise your float bowls are going to overflow and the engine will run rich at anything other than WOT.
Most carb setups - with the exception of what Hornbm is talking about - require that the fuel pressure pump provide a fixed pressure (usually 4-8psi based on carb throat size and bowl size), and this pressure is maintained by the needle valves and seats to set the fuel level in the bowls. Once the bowls are full, any overflow fuel is sent back to the tank via the return line.
If you aren't using a return style regulator, then the fuel pressure will overpower the needle valves and seats and allow the float bowls to fill up completely until they overflow - oftentimes sending this excess fuel right down the intake. This is why you're not seeing any fuel leaks, and also why you're getting such crappy mileage.
The return line should still be in place on your car, you'll just need to run some fuel line from the carb overflow outlet to the return line on the chassis. Good luck, and report back,
i am going to try this later today. if it works, then you will be my saviour for the day,
Last edited by riffraff; 01-02-04 at 01:13 PM.
01-02-04, 02:07 PM
#10
Whack 'em and stack 'em
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When I installed a used 45 DCOE Weber on my 12A it had a return line. However- I could not get the fuel pressure to regulate at the correct psi- max was 1. psi (running a redline weber high flow pump and holley regulator).
I dead headed the return line and the psi is regulated like a rock at just under 4 psi (or wherever I want to set it). I don't seem to be having any flooding problems.
I dead headed the return line and the psi is regulated like a rock at just under 4 psi (or wherever I want to set it). I don't seem to be having any flooding problems.
01-02-04, 03:03 PM
#11
smog nazi destroyer
Thread Starter
so i jumped the gun a little.
what is the best way to setup a return line. should i just put it in series with the feed line , or am i going to have to do some drilling somewhere?
what is the best way to setup a return line. should i just put it in series with the feed line , or am i going to have to do some drilling somewhere?
01-02-04, 05:30 PM
#12
Nikki-Modder Rex-Rodder
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The fuel return in the stock Nikki consists of nothing more than an .40 orifice drilled into the inlet tube where the outlet banjo (return line) slides over it.
It does not actually provide a true unhibited circulation of the fuel.
I think the original return orifice is a very simple flow inhibitor that ensures a build up of a gauranteed minimal pressure in the inlet line.
Remember, the stock pump is a piston type, and there is no "backflow" with this type of "positive" pump.
The carburetor is vented in any case, and flooding can certainly happen with the return line in place, so what does that tell you?
If your needles are jumping open with only 4.5 psi even with no return line, then something else is not right.
It does not actually provide a true unhibited circulation of the fuel.
I think the original return orifice is a very simple flow inhibitor that ensures a build up of a gauranteed minimal pressure in the inlet line.
Remember, the stock pump is a piston type, and there is no "backflow" with this type of "positive" pump.
The carburetor is vented in any case, and flooding can certainly happen with the return line in place, so what does that tell you?
If your needles are jumping open with only 4.5 psi even with no return line, then something else is not right.
Last edited by Sterling; 01-02-04 at 05:36 PM.
10-18-18, 02:00 PM
#13
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The fuel return in the stock Nikki consists of nothing more than an .40 orifice drilled into the inlet tube where the outlet banjo (return line) slides over it.
It does not actually provide a true unhibited circulation of the fuel.
I think the original return orifice is a very simple flow inhibitor that ensures a build up of a gauranteed minimal pressure in the inlet line.
Remember, the stock pump is a piston type, and there is no "backflow" with this type of "positive" pump.
The carburetor is vented in any case, and flooding can certainly happen with the return line in place, so what does that tell you?
If your needles are jumping open with only 4.5 psi even with no return line, then something else is not right.
It does not actually provide a true unhibited circulation of the fuel.
I think the original return orifice is a very simple flow inhibitor that ensures a build up of a gauranteed minimal pressure in the inlet line.
Remember, the stock pump is a piston type, and there is no "backflow" with this type of "positive" pump.
The carburetor is vented in any case, and flooding can certainly happen with the return line in place, so what does that tell you?
If your needles are jumping open with only 4.5 psi even with no return line, then something else is not right.
10-23-18, 10:53 AM
#14
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