Fuel pipes wrong way round

[Wrider]

You’re probably all getting sick of my hopelessness but I tried to start my bike with the fuel pipes the wrong way round after refitting the tank.

Will this have done any damage?

[Darren69]

I wouldn't have thought so, I can't think of anything atm. I fitted QD some couplings to mine so I couldn't fit the lines wrong way and it makes taking the tank off much easier.

[Wrider]

Originally Posted by Darren69

I wouldn't have thought so, I can't think of anything atm. I fitted QD some couplings to mine so I couldn't fit the lines wrong way and it makes taking the tank off much easier.

Hope not!
Recommend any particular ones?
Thanks

[Darren69]

It was many years ago but something like these: -

https://www.ebay.co.uk/itm/Quick-rel...gAAOSwrFtaKVsz

Check that it is 8mm ID pipe.

Mine are white plastic and you can get metal ones for a bit more money but I've had no issues with the plastic ones but don't actually need to disconnect them too often anyway.

[Darren69]

Here's the metal version: -

https://www.ebay.co.uk/itm/TR-Race-S...cAAOSwvKBezp2n

[Wrider]

Turns out I did have them the right way and I have another reason it won’t start.
It’s trying to fire but maybe no fuel is getting through?

[Dukedesmo]

Not sure where the pressure regulator is on your bike?

If in the tank (like a 916) then it matters not which way round the the pipes are, even if they are labelled flow and return (or Mandata and Ritorno) as the fuel line to the injectors is kept at a constant pressure regardless of flow direction.

[Wrider]

I didn’t connect the power commander when I changed the battery! Started straight away. Phew!

[Darren69]

yea, it think it should still run no matter which way around they are, the fuel pressure regulator is there to prevent any damage due to over pressure and it would still work the same but in reverse.The Low tank level sensor would probably take a day off however. If it actually works that is?

[spuggy]

Originally Posted by Darren69

fuel pressure regulator is there to prevent any damage due to over pressure

Actually, no. What you've described would be an over-pressure relief valve. I don't know of any vehicle that has one of these in the fuel system (although everything has at least one - and some have multiple - in the oiling system).

Before the mid-80's, fuel pumps were "roller cell" type; however, almost all modern fuel pumps are "positive displacement", which cannot develop any pressure without a restriction or control in the circuit. Hence the FPR.

Without one, you get flow, but no pressure - the injectors need a certain pressure range to work correctly. 3 bar (or 45 PSI) is pretty typical for EFI.

Carbs generally want a lot less (like 3 PSI or so) - or you tend to overcome the float needles..

The fuel gets continuously pumped (circulated and returned to the tank) both to avoid localized overheating (eg in a fuel rail over the cylinder head) and because the fuel is used to cool and lubricate the pump.

Interestingly (well, I thought it was anyway), very common in turbo systems to use a rising-rate FPR - the regulator has a vacuum reference, that off-sets regulated fuel pressure by the amount of pressure "seen" in the intake manifold. So when there's 1 bar of boost in the intake manifold, the fuel system is regulated to the nominal 3 bar + 1 bar. Which both proportionally provides extra fuel (assuming the injector duty cycle remains the same duration) and maintains the advantage (pressure differential) of the injector over the intake for a good spray pattern.