Rover V8 Twin SU's overflowing petrol

[Nige]

Re-built both my SU's (SD1 Hif6) on my rover v8. New seals, jets, needle valves & seats & o-rings. Car fired up fine after re-installing. I balanced the two carbs with airflow meter so I think thats fine. I also adjusted the screw for setting richness on each of the carbs. I'm told that if its setup right, when you lift the dashpot with the liftpin, the revs should increase slightly and then start dying off. Both carbs seem to be doing this now, so I think are adjusted ok. It starts no problem & idles smoothly.

It drove fine for a few miles, than it started stuttering. Eventually I found out that the overflow pipes on both carbs were pouring out petrol. If I turn off the electric fuel pump, the car runs ok for a few mins until, naturally, it runs out of petrol). If I turn back on the pump and re-start, it can be ok for a while, then it starts pouring out of both over-flows again and starts stuttering. The flow is strong, not just a drip. A strange thing I noticed with the over-flow pipes - while the engine is running normally (nothing coming out of overflow pipes), if I block the overflow pipe, the engine starts to die until I unblock it again. I tried the opposite carb and it does the same. It looks like its breathing through/venting through the overflow pipes??? I doubt this is normal..

The fuel bowl's are obviously overflowing because the petrol is overfilling the bowl. When I installed the new needle valve and seats, I did setup my floats again as spec'd in Haynes manual (approx 1 mm lower than base of carb, when carb held upsidedown). I did have to adjust the float a good bit (bend the little tab on the float), the new needles must have been a little shorter the the old ones.

I have a facet fuel pump, without any fuel pressure regulator. There is no fuel return line from the carb (Dont know where you could fit one to the carb??). I've always been running this way and I never had this problem before...

Do you think adjusting the idle mixture screw could cause this (I cant really see how)?
I doubt both my floats are leaking...both overflow pipes start flowing at the same time, so hardly that?
Fuel pump too much pressure? Same pump I've always had, never had this issue before. Pressure reg needed?
New needle valve combo bad...might not be closing correctly and allowing fuel to keep filling the bowl... most likely?? Are you supposed to do anything with needle valve combo when you install them? Tap the back of the needle to it 'forms' a good seal with seat?

Anything else I could have installed wrong when I was re-building that might cause this. I was very careful to put everything back as it was, so I'm hoping not...

Thanks...

[RoverP6B]

Hello Nige,

Fuel flowing from the overflows when it has happened on my engine was always down to one of the floats being defective,..ie filling with fuel.

In my mind what is happening is all down to not have a spill return connected to return excess fuel to the tank. My Rover runs twin SU HIF6 carburettors, I have both a mechanical and Facet fuel pump, no pressure regulator. With engine idling, switching on the Facet which is in series with my mechanical pump sees no fuel overflowing. Fuel additional to requirements is directed back to the tank. You can see a pic of the spill return on my engine here.....http://www.v8forum.co.uk/forum/viewtopi ... 60&start=0

The only way that I could see being able to run twin SU carbs with no spill return would be to utilise a pump that switches on and off as is appropriate so as to ensure no surplus fuel is delivered. Much better in my opinion to use a spill return.

Adjusting the mixture which as you know is for the idle setting only will as you suspect have no bearing on fuel overflowing. When you raise the lift pins, the idle should increase slightly then essentially return pretty much to where it was, not higher or too much lower.

I can see nothing wrong in the description that you give on what you have carried out on the rebuild.

Ron.

[CastleMGBV8]

Nige,

SU's like approx 3.5psi and depending on which Facet pump you have you could have up to 8psi, the excess pressure could explain your problem.

If the engine is standard then a SU type pump providing 3.5 psi should solve the problem or if a modified engine, you could keep the Facet and fit a pressure regulator to ensure sufficient fuel flow at wide open throttle.

kevin

[marcjagman]

I've got strombergs on mine and they have a fuel return back to the tank.

[Dave3066]

I had this happen very briefly to one of my HIF6s on my Rover. It only happened on the right hand carb and it only happened after I'd replaced the fuel filter. I took the dashpot and piston out and gave the carb a blow through with compressed air. It ran fine after that. I think a small piece of plastic had got lodged somewhere in the carb from having to shave off the shoulder on the fuel filter to get the olive on it. Perhaps you've had some crud in the system that has got into both carbs. Worth a try.

Dave

[Nige]

Thanks for the replies folks...

I will try blowing out the carbs to see if I can dislodge any dirt. The petrol was getting low in the tank, but the tank is new enough and I've ran out lots of times before without getting dirt in the carbs.

One thing that doesnt make sense for me about dirt....should it not be overflowing all the time now, if there's dirt in there? I need to double check, but I'm fairly sure that after I turned the car back on, it idled away there for 10 mins without any overflow??

This is also why the excess fuel pressure doesn't fully make sense for me.... While standing idleing, there was no overflow fuel. Would the fuel pressure at idle not be the highest...the carb would not be using much? Yet, it was only when driving it (using more fuel -> less fuel pressure?) thats when the overflow started happening... Any thoughts?

Do the fuel return lines attach to where the current over-flow pipes currently? I dont see any 'spare' ports to connect up return lines to..

As regards fuel pump, It's a solid state Facet, but I dont know what pressure it puts out. I can't see any markings on it to tell me its model number...I have a photo, but I cant figure out how to attach it here??

What model of King Fuel Pressure Regulator is recommended for 3.5 RV8 engine with twin SU's. I see some high flow 'V8' regulators advertised..anyone recommend a model or where's good to buy one?

Thanks.....

[RoverP6B]

Nige wrote,...

Do the fuel return lines attach to where the current over-flow pipes currently? I dont see any 'spare' ports to connect up return lines to..

No. The overflow pipes are there only to vent the float bowls, and to provide a means of delivering fuel to the ground when a problem occurs.

The pressure from the Facet is constant. It does not change with engine speed. The pump must deliver sufficient fuel so that the bowls are always full regardless of engine load. If the level drops then the engine runs leaner than it should.

This is why a spill return should be used when the pump delivers continuously.

Ron.

[Nige]

I worked on the carbs this weekend...blew them out with compressed air, but made no difference. Still overflowed after. Took them apart and there was no dirt in there. Checked the float height and they were both fine.



Changed out the needle & seats to the old ones which were in it. Setup float heights again. Now, the oveflowing of the carbs isn't happening while driving. (If I leave the pump running long enough with engine switched off, I see a few drops come). It can be a bit stuttery to take full throttle when driving, and now I'm wondering if it's got to do with over pressuring too. It was at this before I re-built the carbs too.. If I lift off the throttle, it starts firing properly again.



I found out my facet fuel pump is a Comp version (model: 40147), with a pressure range of 4.5 to 9 psi. Sounds way too high for the SU's, so I think a pressure regulator is needed (or some type of fuel return system). I was told a Filter King FPR008B regulator would be suitable...Anyone using one of these or is it a suitable regulator for my setup? Is the high flow 'V8' regulators over-kill?



Thanks for the replies...

Nigel

[jimthesail]

Identical problem to mine with a kit car and a Hardi pump (also tried Facet) even using a Malpassi fuel regulator and over height floats (+2mm instead of -1mm). How did it end ?

[stevieturbo]

Identical problem to mine with a kit car and a Hardi pump (also tried Facet) even using a Malpassi fuel regulator and over height floats (+2mm instead of -1mm). How did it end ?

11 years ago lol