Fuel Return line

[Nige]

I have a rover V8 3.5 (twin SU cards) engine which is being fed with a Facet fuel pump. However, it doesn't have any return line for the fuel and I cant see any obvious place on the carbs where it looks like there should be one . Should there be a fuel return line on the standard twin SU's where came on the SD1??

I have problems re-starting the engine every time when its hot (normal running temperature), but it starts every time when the engine is cold. From reading some of the previous threads, could this be caused by vaporisation in my carbs because of excess heat? If I leave the engine for a while to 'cool down', it starts again without hassle. The engine is in a mk1 escort so the engine bay is small and there is a lot of heat. From the description, could vaporisation possibly be my problem??

[5000SE]

I have a rover V8 3.5 (twin SU cards) engine which is being fed with a Facet fuel pump. However, it doesn't have any return line for the fuel and I cant see any obvious place on the carbs where it looks like there should be one . Should there be a fuel return line on the standard twin SU's where came on the SD1??

I have problems re-starting the engine every time when its hot (normal running temperature), but it starts every time when the engine is cold. From reading some of the previous threads, could this be caused by vaporisation in my carbs because of excess heat? If I leave the engine for a while to 'cool down', it starts again without hassle. The engine is in a mk1 escort so the engine bay is small and there is a lot of heat. From the description, could vaporisation possibly be my problem??

First point - you have a fuel return line for injection systems, but not for carbs.

Second point - yes! Vapourisation could be in the fuel line as well as the carbs, it can help to fit a bigger diameter line, or to insulate it.

[Ian Anderson]

Zimbabwean trick when they blended pertol with enhanol it evaporated all the time

Take a piece of mutton cloth or similar and wrap around the fuel pipe in engine bay

Disconnect washer pipe from windscreen and cable tie along the fuel pipe and puncture it along the way

When engine don't start squirt the water and you get instant cooling with the evaporaion effect

So MOT needs squirters so fit a second pump etc. (No MOT tests in Zimbabwe!)

Or you could just insulate the pipe

Also check the fuel pump pressure - could be too low and evaporation is building up enough pressure to "stop" the pump (Clean out filters etc.

Ian

[ramon alban]

I have problems re-starting the engine every time when its hot (normal running temperature), but it starts every time when the engine is cold. From reading some of the previous threads, could this be caused by vaporisation in my carbs because of excess heat? If I leave the engine for a while to 'cool down', it starts again without hassle. The engine is in a mk1 escort so the engine bay is small and there is a lot of heat. From the description, could vaporisation possibly be my problem??

I wrote this after researching the subject for EFI cars to try and find out the reasons for the problem and possible solutions.

Some of the suggested solutions might apply to your carb situation. See what you think

http://www.vintagemodelairplane.com/pag ... art01.html

The confined space you mention is the the most likely cause factor and it may be that you need to introduce flow thro' cooling somehow.

[Nige]

Thanks for the suggestions...
The more I think about it, the more I think it could be vaporisation. What cold, the electronic fuel pump runs at a certain speed and I can hear it change after a few seconds as the pressure builds up. When trying to start it when its hot, the pump races a lot quicker (like what it sounds like when its running out of fuel), possibly suggesting its trying to pump gas (vaporised fuel)?

Would a fuel pressure regulator (Filter King Fuel Pressure Regulator) be of any benefit? I think there is a fuel return line from the the regulator. Would this buy me anything?

[Paul B]

Thanks for the suggestions...
The more I think about it, the more I think it could be vaporisation. What cold, the electronic fuel pump runs at a certain speed and I can hear it change after a few seconds as the pressure builds up. When trying to start it when its hot, the pump races a lot quicker (like what it sounds like when its running out of fuel), possibly suggesting its trying to pump gas (vaporised fuel)?

Would a fuel pressure regulator (Filter King Fuel Pressure Regulator) be of any benefit? I think there is a fuel return line from the the regulator. Would this buy me anything?

Is your pump in the engine bay? If so, you need to move it back to the fuel tank, preferably below fuel level. I had the noisy pump problem when I fitted a Facet to my Morris, and I moved it three times before I bit the bullet and put it out back and low down, and now I hardly ever hear it.

I find it hard to see how fuel vaporisation in the carb can cause hard starting, because the top of the fuel bowl is open to the atmosphere, so as fuel evaporates it will leave the car and disappear into the world. When you turn your electric fuel pump on it will quickly refill the fuel bowl to replace any fuel that said goodbye, and should perform as normal. There would only be a problem when using a mechanical pump that does not operate until you try to start the engine, and then it has to fill the carb as you are cranking it over.

Same with fuel evaporating in the fuel line, it should pump straight through when you turn your pump on. Only solid fuel will lift your floats up, so the needle jets remain open to let any gaseous fuel through.

Assuming you have your fuel pump wired to a switch and not just to come on when your motor is running, or trying to run??

I recently fitted a carb spacer under my Weber 500, and straight away I had real problems starting it after shutting down after a hard run.

Eventually I stripped and cleaned the whole setup, reassembled it, and it starts on the button now, instantly, even when red hot, so I have no real idea what the problem was.

[Nige]

My fuel pump is located in the back of the car. It is low down, under the fuel tank so it is in the lowest position. I have it so it comes on before I start cranking over the engine, so it is pumping before the engine is trying to start.
What you say about the carb re-filling etc makes sense, so I dont know why the pump would be racing/pumping so quick when trying to start it hot? It does seem as if there is very little resistance in the fuel line. Maybe there is something jamming open in the carbs??

[Paul B]

My fuel pump is located in the back of the car. It is low down, under the fuel tank so it is in the lowest position. I have it so it comes on before I start cranking over the engine, so it is pumping before the engine is trying to start.
What you say about the carb re-filling etc makes sense, so I dont know why the pump would be racing/pumping so quick when trying to start it hot? It does seem as if there is very little resistance in the fuel line. Maybe there is something jamming open in the carbs??

Sounds like you are either sucking some air into the fuel system/pump or your carb is emptying from heat and your pump is busy filling it again. If you just turn the pump on when it is all good 'n hot does it keep clatttering for ever, or just a few seconds?

Sometimes fuel can gravitate back down through the pump, leaving your fuel lines empty, or with bubbles in, but sealed at the needle valve, so you are compressing air instead of fuel when you turn the pump on.

Or you can get air bubbles trapped in the pump and until you start flowing fuel the bubble sits inside the pump making noise. Mounting the pump to the correct angle ensures they float up through the pump.

[jwriyadh]

In answer to your original question, I know not whether the SD1 had a fuel return line fitted, most likely but Ramon can tell you that answer.
A fuel return line will cure most vaporisation problems that you may have. As you turn the key to start fresh cool fuel from the tank replaces any vapour in the fuel line, and if necessary refills the carb float chambers.

If you need parts look for any Land Rover fitted with an RV8 on carbs.

Be careful with your choice of pipes and fittings, the return line is deliberately made to flow less than the feed line. The difference in flow rates provides the pressure to fill the carb float chambers.

jw

[badger]

500SE, all landrover variants with carbs have a return line, for this very reason.

As jwriyadh says, either look for the landrover parts or simply fit a t-piece in the fuel rail between the carbs and feed this new offtake through something like a 3mm bore restrictor back to the tank. Don't be tempted to t the return to the inlet of the pump, all you'll do is circulate vapour - it has to go to the tank.

[x.l.r.8]

Land rovers came with a return line to ensure the flow to the floats was constant due to the extreeme angles they were designed to run at. If you fit a return line you wnat it as close to the carbs as possible, then I use a Nitrous jet to restrict the flow back. In your case the result will be questionable.
I always question the possibility to overfueling, cold engines love additional fuel so will have no issues, but warm engines will flood quickly and be very hard to start, especially if you have a heavy foot. A mk1 will put the system very close to the starter and hot starters do not turn over very well unless you have a hi-torque one. Another thing to check is air flow, again a cold engine will tollerate less air flow richening to mixture, but a warm engine won't.

[jrv8]

In answer to your original question, I know not whether the SD1 had a fuel return line fitted, most likely
jw

The SD1 carb set up did not have a return line fitted.

I agree with x.l.r.8 that the problem could well be caused by an over-rich mixture. Fuel evaporation was never an issue with the SU carbs on an SD1
Regards
Jim

[Nige]

Thanks for the suggestions..
The idea about the starter motor not working well may also be something to do with it. If the car is hot and it wont start, I can put a set of jump-leads onto a running car and it will fire almost straight away. You can hear the engine turning over quicker with the jumpleads on. (I did swap a battery from a new car into it but it didnt make a difference, so I dont think its a battery issue). Somehow the extra voltage (14.4V from running car) does make it start. Not sure if its the starter turning quicker or perhaps better voltage at coil (better spark) which helps it start??

[Alley Kat]

My last car had twin SUs, no return line, and started fine hot or cold. (Can't see why a road car on carbs needs a return line, except mebbe to mask some other issue)

Are the carbs properly set up, in good nick, clean, balanced etc. Cold start setup all OK ?

What Facet is it, or rather what pressure is it putting out. Someone here will know but thought SUs liked quite low pressure (3.5 or 4lbs?)

Has it always done this, or has some new component been added?

To eliminate the bay temps side, is it worth raising the bonnet up a bit at the back, temporarily (spacers/washers), as a test to let heat escape?

[Nige]

The car been doing this for as long as I've had it. The problem didn't just switch on after changing something. I will try raising the back of the bonnet to help let hot air out and see if it makes a difference.

The fuel pump is Facet Solid State (square shaped) pump. I dont have the model number to hand to check what fuel pressure it puts out. The label on the end of the pump is in blue, maybe that signifies a particular type? I think these Solid State type are lower pressure than the cylindrical type you see on some cars.

The carbs have recently been setup on the rolling road by a professional and new needles (richer) installed. The carbs were balanced etc during this setup. I assume my cold start setup is ok because it does start fine when cold...or is this a wrong assumption?? . The guy at the rolling road did mention that the seals on the carbs were a bit worn, because the dashpots use a lot of oil and empty themselves quickly, even with heavier oil. He recommended getting them re-furb'd but i haven't come across a re-build kit yet...