Triumph Vitesse – Fuel line shape and routing

[Jason C]

20 hours ago, RobPearce said:

It doesn't matter terribly much - whatever fits the pump best.

Thanks Rob, it should be fine. 👍🏻

[Nick Jones]

1 hour ago, Jason C said:

Thanks Rob, it should be fine. 👍🏻

All else being equal, I’d suggest 5/16” or 8mm pipe wherever possible on the suction side of the pump (ie. between tank and pump) to minimise suction losses. Every little helps stave off vapourisation.

Nick

[Jason C]

Hi @Nick Jones interesting! OK, while I’m replacing may as well upgrade to 5/16" from the tank, along the main fuel line. Assume the metal spring clips on the chassis are the same and accept the slightly larger diameter pipe? Could you please go into some detail on ‘suction loss’ and ‘vaporisation’? My limited understanding is the larger pipe helps with density of fuel, more capacity in the line with the pressure remaining the same. With suction loss - more fuel readily available in the line, no searching for fuel as such?

[Nick Jones]

Liquid, even thin liquid, travelling through pipes experience friction with the walls of the pipe and internal friction from turbulence within the fluid. This is proportional to the velocity of the fluid travelling through the pipe. This “suction loss” means the pump has to suck harder which lowers the pressure at the pump inlet valve in particular.

Therefore using a larger pipe reduces the losses and means the system can move fuel without lowering the pressure in the suction line so much.

This matters, as one of the factors (along with temperature and turbulence) that causes fuel to boil (vapourise) is low pressure.

Every little helps. And yes, the bigger pipe does fit in the same metal clips.

Nick

[Jason C]

36 minutes ago, Nick Jones said:

Liquid, even thin liquid, travelling through pipes experience friction with the walls of the pipe and internal friction from turbulence within the fluid. This is proportional to the velocity of the fluid travelling through the pipe. This “suction loss” means the pump has to suck harder which lowers the pressure at the pump inlet valve in particular.

Therefore using a larger pipe reduces the losses and means the system can move fuel without lowering the pressure in the suction line so much.

This matters, as one of the factors (along with temperature and turbulence) that causes fuel to boil (vapourise) is low pressure.

Every little helps. And yes, the bigger pipe does fit in the same metal clips.

Nick

Thanks so much for the fantastic explanation @Nick Jones great advise. Will use the larger diameter fuel line.
 

A supplementary question about fluid dynamics, is it a bad idea having a fuel filter just before the fuel pump? Would this reduce pressure? Or beneficial as a safe guard, my filter doesn’t appear to be trapping many particulates visible to the naked eye.  
 

Do you have a preference for steel or Kunifer pipe? Kunifer looks easier to work. We don’t use salt on our roads so rusting not as much an issue. I imagine steel is more rigid across the main length - but it is clipped quite frequently. 

[Rosbif]

56 minutes ago, Jason C said:

is it a bad idea having a fuel filter just before the fuel pump?

I, for one, have a filter just before the pump. No problems, in fact it seems a lot of owners put one there. I just use the cheap plastic ones and when they get opaque replace them, not because it affects their efficiency I treat it as a 'service interval' 

[Nick Jones]

Would struggle to buy steel (Bundy) in the UK. 

I use Kunifer for first choice but wouldn’t worry about copper either if properly clipped. Not perhaps an option for you in NZ for legal reasons? Or is that OZ….?

Filter has the potential to cause losses, but maybe essential to prevent other issues.  Should be ok so long as it’s big enough.  Can become an issue over time as it does its job and gets clogged. Useful to have one with a clear housing so you can keep an eye on what’s happening inside it.

On my FI setups I have a relatively coarse strainer before the pump and a proper fine high pressure filter afterwards.  Different needs though.

Nick

[Jason C]

39 minutes ago, Rosbif said:

I, for one, have a filter just before the pump. No problems, in fact it seems a lot of owners put one there.

Good to hear, thanks @Rosbif. The car currently has one too and seemed fine (when it was running). Seems a good stop gap if anything comes through from the tank. Although the petrol pump has a filter, but not as fine as a fuel filter. 
Mine likely needs replacing, I’ve flushed it out, but it’s old as the hills. 

[Jason C]

38 minutes ago, Nick Jones said:

Would struggle to buy steel (Bundy) in the UK. 

I use Kunifer for first choice but wouldn’t worry about copper either if properly clipped. Not perhaps an option for you in NZ for legal reasons? Or is that OZ….?

I’m back in NZ, where I think copper isn’t legal from what I understand. Same with Australia. Bundy is easy get a hold of, (had some brake pipe bent by a specialist a few months back) so one assumes it’s legal.  
 

Kunifer looks harder to source, around $100 NZD for 12ft. Pricey but likely easier to bend around tank and engine bay sections. 

44 minutes ago, Nick Jones said:

Should be ok so long as it’s big enough.

For filter size, guess it’s not just a matter of finding one with 5/16inch fittings, size based on pressure that’s being pushed through it? 

[Jason C]

On 11/12/2021 at 23:15, Nick Jones said:

All else being equal, I’d suggest 5/16” or 8mm pipe wherever possible on the suction side of the pump (ie. between tank and pump) to minimise suction losses.

Sorry @Nick Jones another question, how does one handle the the 1/4" pick-up tube – to 1/4" fuel hose – transitioning to 5/16" sized line? Is there appropriate fitting? Or did Triumph clamp the 5/16" very tightly to the fuel tank? Although, I’m especially wanting an excellent seal within the boot cavity to prevent any potential odour. 

[Rutty]

2 hours ago, Jason C said:

 how does one handle the the 1/4" pick-up tube – to 1/4" fuel hose – transitioning to 5/16" sized line? Is there appropriate fitting? Or did Triumph clamp the 5/16" very tightly to the fuel tank?

 

My MK1 Vitesse has had the under body fuel line replaced with 5/16 at sometime in its past so I have 1/4 from tank 5/16 under the body, back to 1/4 into the fuel pump and 1/4 from the pump to the carbs. The previous owner had just used 1/4 fuel hose and forced it onto the 5/16 fuel pipe. When I replaced the fuel hose with ethanol proof hose I used the appropriate size hose for the pipe and brought 1/4 to 5/16 brass adaptors off Ebay to connect the 1/4 to 5/16 hose together. 

Mark

[Jason C]

15 hours ago, Rutty said:

My MK1 Vitesse has had the under body fuel line replaced with 5/16 at sometime in its past so I have 1/4 from tank 5/16 under the body, back to 1/4 into the fuel pump and 1/4 from the pump to the carbs. The previous owner had just used 1/4 fuel hose and forced it onto the 5/16 fuel pipe. When I replaced the fuel hose with ethanol proof hose I used the appropriate size hose for the pipe and brought 1/4 to 5/16 brass adaptors off Ebay to connect the 1/4 to 5/16 hose together. 

Mark

Thanks Mark, sounds like an elegant solution. I‘ve found a few brass inline joiners for fuel hose after looking into your idea. The other idea I had was to use an inline fuel filter as the joiner, one end with 1/4 the other as 5/16. However, having the fuel filter hidden way behind the fuel tank is not the most accessible location – but I assume they are good for a lot of miles.

Speaking of fuel filters, paper filter 10microns the standard? I have seen a fancy sintered bronze element filter that filters down to 40microns. At what level does it start reducing flow I wonder?

 

[RobPearce]

1 hour ago, Jason C said:

The other idea I had was to use an inline fuel filter as the joiner, one end with 1/4 the other as 5/16.

That's a good option at the pump end, if you need to. It's not so convenient at the tank.

1 hour ago, Jason C said:

Speaking of fuel filters, paper filter 10microns the standard? I have seen a fancy sintered bronze element filter that filters down to 40microns. At what level does it start reducing flow I wonder?

The filter element is a very large area, so it doesn't actually cause that much resistance to flow. I've always put a paper filter (the cheap transparent plastic type) just before the pump on all of mine (well, except the Spitfire, which has a glass bowl "separator" before the electric pump and a posher filter after) and never had any problems.

[Jason C]

5 hours ago, RobPearce said:

(well, except the Spitfire, which has a glass bowl "separator"

Thanks @RobPearce for the tips. Your note about the glass bowl, raised another thought – how well does the brass mesh filter inside the AC mechanical pump work? It doesn’t look incredibly fine, nor would be as good as paper. Guess at the time Triumphs fuel filter in the one unit?  

[RobPearce]

4 minutes ago, Jason C said:

how well does the brass mesh filter inside the AC mechanical pump work?

Well enough that they can get clogged up! I had that on my (relatively low mileage at the time) Toledo shortly after I bought it. I went to drive up the road and it wouldn't accelerate. The mesh is cleanable but requires dismantling of the pump. I fitted a plastic/paper filter before the pump after that - the orientation is such that they're less prone to clogging as well as more effective.

[Jason C]

1 minute ago, RobPearce said:

Well enough that they can get clogged up!

Ha yes! Very good point, it must have been the thought that counts thinking from Triumph. I’ve found the hanging glass design a little easier to remove without fuel drops.
 

Will add a new transparent filter to the line before the pump. 👍🏻 

[Pete Lewis]

know one has mentioned the chance of making those nasty rubber slivers  these are small slices of hose thet can get cut off by inserting metal pipes and they float about in the lines and will eventually block the back of the float needle valves 

its worth being aware with all the messing about with the pipe run will get these crafty little sods to breed and give you a surprised misfire when you dont want it 

it happens a lot , less with high quality hose but they are out there 

waiting to get you annoyed 

Pete

 

[Jeffds]

Pete loves his little slivers!

Just to add some info., my later 13/60 has the same tank as the vitesse with 5/16 pipe outlet which passes through the floor and then narrows to 1/4 pipe all the way to the carb. The hose at the junction is just tightened more on the 1/4 

I had fuel starvation after a short layup and suspected the pump, so 30 quid later, new pump in place... I still had starvation!!

I eventually siphoned fuel through and he ran. 🙂 great... no it wasn't.....fuel peeing out of carb!

New pump pressure was 4psi. Far too much. 2 is more than enough. I then found bubbles, seen in the filter just before the pump. Found the 'loop' hose out the top of tank was letting air in. It was 5/16 and I only had 1/4 so trimmed the perished ends and refitted. Replaced old pump and all is good now 🙂

rimmers even sent me 2nd 4psi pump when I moaned.... I have therfore got a spare spare if anyone needs one. ( mind you will need a pressure regulator!!)