Return Fuel Line Restrictor

Grey V8 Pete · #1 10th April 2012, 22:55

Does anyone with fuel injection BMW in a Sportster with a fuel swirl pot, have a restrictor fitted in the return line to the tank?

I notice on one of the RPI (V8) links that they recommend blanking off the return line to avoid under fuelling at high throttle openings. Although this probably refers to carbs it has set me thinking if the same is true for fuel injected engines using a swirl pot.

For the low pressure line to my Rover V8 3.9I I have a Pacet Red Top pump supplying the swirl pot. The delivery and return pipes are 8mm bore and as far as I can tell the LP pump is churning fuel around the system at a fair rate of knots.

During one of the Marlin runs someone following me in a Sportster commented that my car smelled of petrol fumes but no leaks have been found anywhere since. I am wondering if all the LP pump activity is aereating / vaporising the fuel so maybe a restrictor in the return line would ease the pump activity whilst still providing enough circulation to cool the fuel supply. Peter.

chrislandy · #2 11th April 2012, 20:21

If you run injection then you should have a fuel pressure regulator at the end of the injector rail, this effectively acts as the return restrictor on the fuel delivery system.

The swirl pot should be plumbed into the low pressure system, the point being that at full tilt and going round a corner the fuel should not run out to the HP pump so should be sized to suit the engine.

I've got the Shelsley plumbed up that way and not had vaporisation problems due to the pump activity, mine has problems due to a very hot engine bay and the fuel vaporising when stationary

Grey V8 Pete · #3 12th April 2012, 22:31

The fuel pressure regulator only affects the HP line. It's the return line to the tank from the swirl pot that I was considering restricting. The red top Pacet is recommended for the V8 engine size.

However I have since found the following link about this subject which make interesting reading. It seems that my LP pump is designed to run 24/7.
Still wondering about my alleged fumes smell though.

http://www.british-cars.net/mgb-gt-v...3092122629.htm

Peter.

peterux · #4 13th April 2012, 21:30

My return from the swirl pot goes straight back to the tank with no restrictor.

Is your fuel tank vent working OK?

I've fitted one of these......

http://www.merlinmotorsport.co.uk/p3...duct_info.html

"Newton fuel tank valve with 1/4 push on unions. A fuel tank valve that allows; 1) air to replace fuel used. 2) air to escape due to heat expansion. 3) a positive shut off to prevent fuel escape due to splashing or roll over. This is acheived by a two ball system. Valve must be mounted vertically."

Grey V8 Pete · #5 13th April 2012, 23:39

Quote:

Originally Posted by peterux

My return from the swirl pot goes straight back to the tank with no restrictor.

Is your fuel tank vent working OK?

I've fitted one of these......

http://www.merlinmotorsport.co.uk/p3...duct_info.html

"Newton fuel tank valve with 1/4 push on unions. A fuel tank valve that allows; 1) air to replace fuel used. 2) air to escape due to heat expansion. 3) a positive shut off to prevent fuel escape due to splashing or roll over. This is acheived by a two ball system. Valve must be mounted vertically."

My vent pipe goes into the filler neck via a small valve the size of a cotton reel. It looks like the one I had on my old Sierra. How can I tell if it is working correctly? Peter.

Sarboy · #6 20th April 2012, 18:56

Hi Pete, I installed a Vulcan 2.1 EFi in my Berli. I fitted the 1.5 Litre swirl pot from Merlin which is fed, from the tank by a, continuously running, red top solid state pump. I have an adjustable fuel line pressure regulator on the fuel rail which returns to the swirl pot.
The pot has four connections. An 8mm (with filter)from tank & LP pump a 6mm return to the fuel tank from the top of the pot, an 8mm return from the fuel pressure regulator and a 15mm feed to the HP (Bosch) injector pump.
The idea is that the red top primes the swirl pot at start and tops it up in normal operation. The fuel regulator returns unused fuel rail fuel to the swirl pot. The 6mm return to tank from the pot gets rid of the (hopefully) excess fuel supplied by the red top. I have had no snags with this system.
I admit that I was aware that I was sort of recycling warm fuel but I have a fair length of copper pipe both to the rail and back to the swirl pot which should allow returning fuel to cool.
I have a flip/flop latched relay inserted in the lp prime pump circuit so that if the car has not run for a while I select AUX on the ign switch and press a button which latches the relay to allow the prime pump to fill the swirl pot prior to starting. Pressing the button again or selecting ignition on and start disengages the relay to allow the prime pump to be powered from the EFi module's injector pump relay. Used it today after a 30 day lay off and the engine started instantly with no churning. Anyway, I've rabbitted on enough methinks!
I hope some of this may help. Cheers for now.

Grey V8 Pete · #7 20th April 2012, 19:48

Quote:

Originally Posted by Sarboy

Hi Pete, I installed a Vulcan 2.1 EFi in my Berli. I fitted the 1.5 Litre swirl pot from Merlin which is fed, from the tank by a, continuously running, red top solid state pump. I have an adjustable fuel line pressure regulator on the fuel rail which returns to the swirl pot.
The pot has four connections. An 8mm (with filter)from tank & LP pump a 6mm return to the fuel tank from the top of the pot, an 8mm return from the fuel pressure regulator and a 15mm feed to the HP (Bosch) injector pump.
The idea is that the red top primes the swirl pot at start and tops it up in normal operation. The fuel regulator returns unused fuel rail fuel to the swirl pot. The 6mm return to tank from the pot gets rid of the (hopefully) excess fuel supplied by the red top. I have had no snags with this system.
I admit that I was aware that I was sort of recycling warm fuel but I have a fair length of copper pipe both to the rail and back to the swirl pot which should allow returning fuel to cool.
I have a flip/flop latched relay inserted in the lp prime pump circuit so that if the car has not run for a while I select AUX on the ign switch and press a button which latches the relay to allow the prime pump to fill the swirl pot prior to starting. Pressing the button again or selecting ignition on and start disengages the relay to allow the prime pump to be powered from the EFi module's injector pump relay. Used it today after a 30 day lay off and the engine started instantly with no churning. Anyway, I've rabbitted on enough methinks!
I hope some of this may help. Cheers for now.

Many thanks for this info. I may well try putting a 6mm restrictor in the return line just to see if it makes any difference.
My set up is verys similar in principle to yours albeit Rover V8 injection with the Lucas 14 CUX ECU. I fitted the RPI Optimax chip to the ECU which is far superior to the OE Land Rover Disco chip (designed for a 2 ton Land Rover) and the Optimax has a couple of useful built in features. When you turn the ignition on the LP and HP fuel pumps prime for a few seconds then switch off. When you turn the key to the start position the engine turns for about four seconds before any signal goes to the ignition (plugs) circuit. This is to help get some oil pressure up before the engine fires. I thought that was a nifty idea. Peter.

Sarboy · #8 21st April 2012, 19:20

Hi Pete - a bit of duff gen from me. The swirl pot was obtained from concept racing. They supply them and arrange the pipework to individual requirements.
Do you send the return from the injection pressure relief/control valve back to the tank or the swirl pot. I do the latter which gives the priming pump a bit of a breather as it doesn't need to keep filling the swirl pot; just topping it up. The swirl pot has a 6mm connection to prevent overfilling and pressurisation. This feeds back to the tank.
Your system that permits positive oil pressure prior to ignition is a good idea. I know of some systems where the oil pressure switch energises/de-energises the power to the Injection pump relay to the same effect.
Cheers.

Grey V8 Pete · #9 21st April 2012, 23:05

My return from the fuel pressure regulator goes into the swirl pot. There is a feed to that from the tank via the Red top L/P pump and the swirl pot vents back into the tank. So does that mean that your swirl pot has 6mm pipes on both the delivery and return pipes from / to the tank? Peter.

Sarboy · #10 22nd April 2012, 13:22

No Peter, the supply pipes are 8mm, The return from the fuel rail is 8mm, the return to tank from the swirl pot is 6mm. (The feed to the HP pump is 15mm). The only 6mm is the final return to the tank. It seems to work OK and I have not had any overpressure problems yet.

Grey V8 Pete · #11 22nd April 2012, 19:16

Quote:

Originally Posted by Sarboy

No Peter, the supply pipes are 8mm, The return from the fuel rail is 8mm, the return to tank from the swirl pot is 6mm. (The feed to the HP pump is 15mm). The only 6mm is the final return to the tank. It seems to work OK and I have not had any overpressure problems yet.

Many thanks. Will try a 6mm reducer in my return line sometime. Peter.