Most fluid regulators have one Inlet, one Outlet, and one Vacuum connectors. The Inlet receives fuel from the fuel pump. The Outlet sends fuel to the carburators/injector nozzles. The Vacuum is a skinnier port that senses AIR pressure from the intake manifold, and it’s always mounted in the same piece as the adjusting screw (left side in this picture).
Usually, the (pressure-regulated) outlet is the one opposite to the adjusting screw. Accordingly, the pressure gage reads only the outlet port.
Some units have a metallic mesh filter. When this happens, that one is without any doubt the inlet port.
When installing this regulator, keep the adjustment screw pointing upward. This is done to reduce fuel spills into the intake manifold in the event of diaphragm failure.
Thanks Alexander. That’s just the information I needed.
As I see it, the vacuum reduces the pressure. In other words, at idle you get high vacuum and lower pressure.
Since this motor came from a bike with a tank mounted pump and regulator, should I assume that the vacuum attachment in not necessary?
Alex
You really need the vacuum attachment in place. Please open this link in a new window:
In the schematic, you’ll see how the diaphragm has a valve that’s normally closed via the spring. When the engine starts working, the vacuum pulls the diaphragm, thus opening the valve. If you don’t connect the vacuum-sensing hose to the inlet manifold, the fuel valve will be permanently closed!
The pressure regulator seen in the graphic has a spring with a fixed pulling force value. Your regulator has an adjustment screw that allows the unit to be installed in different engines.
Interesting that the diagram shows a ‘return to tank’ connection. I have seen it both ways. That is using the regulator as a ‘pressure release’ (after the fuel rail) and as a regulator (before the fuel rail).
As a pressure release, I’d have to run a return. As a regulator, no return to tank should be necessary.
As for the vacuum, if it works the way you describe, Alexander, I wonder how the engine would start if there’s no vacuum and therefore no fuel, would that first crank be enough to get some fuel into the cylinders?
I just realized I might have gave you a faulty set of instructions. Keep reading, please.
In older engines the fuel pressure valve was between the fuel pump and the carburetor, but since motorbikes often have not one but a row of syncronized carburetors you might have a “fuel rail” assembly instead; not much different than those used in fuel-injected engines. In these cases, the fuel pressure valve sits downstream the fuel rail.
In this case, the valve inlet is AFTER the fuel rail, the valve outlet purges fuel to the fuel tank, and the vacuum line is still connected to the inlet manifold. Refer to this schematic for help: http://tuneyourharley.com/biketech/node/7
Sorry for the inconvenience. Better late than never!.
BTW, if you don’t install the vacuum sensing hose, the pressure valve will still be permanently closed so the fuel system will be always working under full pressure. In other words, the injectors will always be shooting fuel as if it were going full throttle even when idle, causing the engine to stall.
No apology necessary, Alexander. I’m grateful for your help here.
Couldn’t get the diagram to come up. Probably because I’m not a member. Couldn’t find how to sing up either but I think I got it.
On the diagram in the manual, the pump and regulator are in the tank and only one (high pressure) hose is connected to the tank. So no return line or vacuum line used.
Additionally, there is only one connection to the fuel rail so pressure is regulated going in, not as a pressure release.
I suppose I can try all this with compressed air. Since my fuel pump puts out 140psi, I can hook air to the “in”, block the “out” and use a hand vacuum pump to test the operation.
As you can see, the spring keeps the diaphragm valve closed. When the engine starts, the air pressure in the intake manifold literally sucks the diaphragm up, opening the valve. That’s what makes me think the outlet port is the one opposite to the adjustment screw while the inlet is the one opposite to the pressure gage. In your valve, the adjustment screw simply presses down the spring to vary its force over the diaphragm.
Your testing idea of using compressed air is a sound one since using water will corrode everything in the fuel system. What you can test here is which port is the outlet. In a few words, you shouldn’t have air exiting the valve if there’s no suction in the vacuum port. As soon as you suck a little in the vacuum port, air will exit the valve. This would also be a good time to adjust the spring tension to your engine’s specifications.
If you can’t use the bike’s original fuel pump+regulator, you’ll need to do a system similar to this one: http://tinyurl.com/c733544
If the bike’s manual doesn’t show a return line it’s probably because the entire pump+regulator assembly sits submerged inside the fuel tank, so instead of running a return line the valve just discharges the excess back into the tank. That’s why it’s recommended to keep the fuel tank over the 1/4 level: less than that can cause bubbles to get into the fuel system through the pressure relief port.
Yes, it does. Thing is, the vacuum port doesn’t do ANYTHING to regulate pressure. Its mission is not to open the fuel pressure valve but to CLOSE IT when the engine has stopped. Keep reading.
In these valves, the spring is calibrated to open the valve at a suggested maximum value, relieving the excess pressure back to the tank. So, these are not regulating devices but relief valves instead, not much different than the ones installed in pressure-cookers.
Here’s the tricky part: once the engine has been stopped, fuel pressure needs to be kept up until it’s time to start it again. Otherwise the pressure would decay slowly over time, and there won’t be enough when you need to start it next morning. And that is what the diaphragm is there for: to close the valve when the engine stops, ensuring proper fuel pressure for the next start.
When the engine is running there’s suction in the inlet manifold because the cylinders are sucking air. The only time the inlet manifold is at ambient pressure is when the engine is NOT working, so that is a positive signal to tell the fuel valve that the engine has stopped.
Electronic Fuel Injected cars have replaced this valve with a small electric pump that raises fuel pressure just before the start. You can hear it next time you’re ready to turn on an EFI-equipped car: it’s the high-pitched “whirrrr” coming from the gas tank once you turn the ignition key to the ON position (before turning it to the spring-loaded START position).
Non-EFI engines can’t rise fuel pressure up to operating levels until the engine-driven main fuel pump does it. To counteract this fact the fuel pressure valve closes its outlet once it senses the engine has stopped, keeping fuel pressure within limits, ready for the next starting.
Of course, turbo/supercharged engines operate ABOVE ambient pressure, but that’s a whole different ball game…
Please read my latest on this under a new subject. Couldn’t figure out hot to reply here with a photo.
Guess I don’t have that concern since mine is an EFI engine and I have an electric fuel pump and, since the fuel pump and regulator are mounted in the tank on the bike this engine came from and since there is no vacuum line running to the fuel tank, there is no expectation of increased pressure as a result of engine RPM.
Therefore, I guess I won’t use vacuum. I’ll mount the pump and regulator beside the fuel tank and add a return line to the tank. That should do it.
So you already had the original pump and regulator? That makes life so much easier! Just make sure they always have fuel in the ports to avoid air to get into the lines, and presto!
One question: carburated bikes rely on gravity for feeding the fuel into the engine. Do you know for sure yours have the fuel pump working full time? Does it have some form of refrigeration, such as air cooling vents?
No, never had the original. Just the manual and the Internet. The original was mounted in the bottom of the tank so I’d have to do a lot of mods to use it. I’ve thought about that a lot though.
Once I have the system primmed, I shouldn’t have any trapped air issues.
I don’t know if the original pump worked full time ( though I suspect it did). My new pump does not have any cooling bit it is intended to be chassis mounted. I’ll need to keep an eye on it but suspect that the fuel bypass will cool it.
If the fuel pressure reg. Is faulty will the symptoms be running out of fuel? My 3.8 v6 Olds 1989 , just stops! No stumbling.starts right back up, runs fine, then drive a few minutes& dies again!
vortexgreenmachine 
Most fluid regulators have one Inlet, one Outlet, and one Vacuum connectors. The Inlet receives fuel from the fuel pump. The Outlet sends fuel to the carburators/injector nozzles. The Vacuum is a skinnier port that senses AIR pressure from the intake manifold, and it’s always mounted in the same piece as the adjusting screw (left side in this picture).
Usually, the (pressure-regulated) outlet is the one opposite to the adjusting screw. Accordingly, the pressure gage reads only the outlet port.
Some units have a metallic mesh filter. When this happens, that one is without any doubt the inlet port.
When installing this regulator, keep the adjustment screw pointing upward. This is done to reduce fuel spills into the intake manifold in the event of diaphragm failure.
Thanks Alexander. That’s just the information I needed.
As I see it, the vacuum reduces the pressure. In other words, at idle you get high vacuum and lower pressure.
Since this motor came from a bike with a tank mounted pump and regulator, should I assume that the vacuum attachment in not necessary?
Alex
You really need the vacuum attachment in place. Please open this link in a new window:
In the schematic, you’ll see how the diaphragm has a valve that’s normally closed via the spring. When the engine starts working, the vacuum pulls the diaphragm, thus opening the valve. If you don’t connect the vacuum-sensing hose to the inlet manifold, the fuel valve will be permanently closed!
The pressure regulator seen in the graphic has a spring with a fixed pulling force value. Your regulator has an adjustment screw that allows the unit to be installed in different engines.
Interesting that the diagram shows a ‘return to tank’ connection. I have seen it both ways. That is using the regulator as a ‘pressure release’ (after the fuel rail) and as a regulator (before the fuel rail).
As a pressure release, I’d have to run a return. As a regulator, no return to tank should be necessary.
As for the vacuum, if it works the way you describe, Alexander, I wonder how the engine would start if there’s no vacuum and therefore no fuel, would that first crank be enough to get some fuel into the cylinders?
I just realized I might have gave you a faulty set of instructions. Keep reading, please.
In older engines the fuel pressure valve was between the fuel pump and the carburetor, but since motorbikes often have not one but a row of syncronized carburetors you might have a “fuel rail” assembly instead; not much different than those used in fuel-injected engines. In these cases, the fuel pressure valve sits downstream the fuel rail.
In this case, the valve inlet is AFTER the fuel rail, the valve outlet purges fuel to the fuel tank, and the vacuum line is still connected to the inlet manifold. Refer to this schematic for help: http://tuneyourharley.com/biketech/node/7
Sorry for the inconvenience. Better late than never!.
BTW, if you don’t install the vacuum sensing hose, the pressure valve will still be permanently closed so the fuel system will be always working under full pressure. In other words, the injectors will always be shooting fuel as if it were going full throttle even when idle, causing the engine to stall.
No apology necessary, Alexander. I’m grateful for your help here.
Couldn’t get the diagram to come up. Probably because I’m not a member. Couldn’t find how to sing up either but I think I got it.
On the diagram in the manual, the pump and regulator are in the tank and only one (high pressure) hose is connected to the tank. So no return line or vacuum line used.
Additionally, there is only one connection to the fuel rail so pressure is regulated going in, not as a pressure release.
I suppose I can try all this with compressed air. Since my fuel pump puts out 140psi, I can hook air to the “in”, block the “out” and use a hand vacuum pump to test the operation.
Opinion?
Copy this URL on a new window to see the regulator diagram: http://tinyurl.com/84dw93y
As you can see, the spring keeps the diaphragm valve closed. When the engine starts, the air pressure in the intake manifold literally sucks the diaphragm up, opening the valve. That’s what makes me think the outlet port is the one opposite to the adjustment screw while the inlet is the one opposite to the pressure gage. In your valve, the adjustment screw simply presses down the spring to vary its force over the diaphragm.
Your testing idea of using compressed air is a sound one since using water will corrode everything in the fuel system. What you can test here is which port is the outlet. In a few words, you shouldn’t have air exiting the valve if there’s no suction in the vacuum port. As soon as you suck a little in the vacuum port, air will exit the valve. This would also be a good time to adjust the spring tension to your engine’s specifications.
If you can’t use the bike’s original fuel pump+regulator, you’ll need to do a system similar to this one: http://tinyurl.com/c733544
If the bike’s manual doesn’t show a return line it’s probably because the entire pump+regulator assembly sits submerged inside the fuel tank, so instead of running a return line the valve just discharges the excess back into the tank. That’s why it’s recommended to keep the fuel tank over the 1/4 level: less than that can cause bubbles to get into the fuel system through the pressure relief port.
But when the vacuum lifts the diaphragm, doesn’t that LOWER the pressure at the fuel rail?
Yes, it does. Thing is, the vacuum port doesn’t do ANYTHING to regulate pressure. Its mission is not to open the fuel pressure valve but to CLOSE IT when the engine has stopped. Keep reading.
In these valves, the spring is calibrated to open the valve at a suggested maximum value, relieving the excess pressure back to the tank. So, these are not regulating devices but relief valves instead, not much different than the ones installed in pressure-cookers.
Here’s the tricky part: once the engine has been stopped, fuel pressure needs to be kept up until it’s time to start it again. Otherwise the pressure would decay slowly over time, and there won’t be enough when you need to start it next morning. And that is what the diaphragm is there for: to close the valve when the engine stops, ensuring proper fuel pressure for the next start.
When the engine is running there’s suction in the inlet manifold because the cylinders are sucking air. The only time the inlet manifold is at ambient pressure is when the engine is NOT working, so that is a positive signal to tell the fuel valve that the engine has stopped.
Electronic Fuel Injected cars have replaced this valve with a small electric pump that raises fuel pressure just before the start. You can hear it next time you’re ready to turn on an EFI-equipped car: it’s the high-pitched “whirrrr” coming from the gas tank once you turn the ignition key to the ON position (before turning it to the spring-loaded START position).
Non-EFI engines can’t rise fuel pressure up to operating levels until the engine-driven main fuel pump does it. To counteract this fact the fuel pressure valve closes its outlet once it senses the engine has stopped, keeping fuel pressure within limits, ready for the next starting.
Of course, turbo/supercharged engines operate ABOVE ambient pressure, but that’s a whole different ball game…
Please read my latest on this under a new subject. Couldn’t figure out hot to reply here with a photo.
Guess I don’t have that concern since mine is an EFI engine and I have an electric fuel pump and, since the fuel pump and regulator are mounted in the tank on the bike this engine came from and since there is no vacuum line running to the fuel tank, there is no expectation of increased pressure as a result of engine RPM.
Therefore, I guess I won’t use vacuum. I’ll mount the pump and regulator beside the fuel tank and add a return line to the tank. That should do it.
So you already had the original pump and regulator? That makes life so much easier! Just make sure they always have fuel in the ports to avoid air to get into the lines, and presto!
One question: carburated bikes rely on gravity for feeding the fuel into the engine. Do you know for sure yours have the fuel pump working full time? Does it have some form of refrigeration, such as air cooling vents?
No, never had the original. Just the manual and the Internet. The original was mounted in the bottom of the tank so I’d have to do a lot of mods to use it. I’ve thought about that a lot though.
Once I have the system primmed, I shouldn’t have any trapped air issues.
I don’t know if the original pump worked full time ( though I suspect it did). My new pump does not have any cooling bit it is intended to be chassis mounted. I’ll need to keep an eye on it but suspect that the fuel bypass will cool it.
If the fuel pressure reg. Is faulty will the symptoms be running out of fuel? My 3.8 v6 Olds 1989 , just stops! No stumbling.starts right back up, runs fine, then drive a few minutes& dies again!