MU Return Pipe

[iani]

I have recently changed my fuel pump over to a sytec pump and removed the Lucas equipment, this included removing a solid steel pipe that ran from the original filter housing to a vent hole next to the filler tube. As I say, this was a solid pipe for all of its length, no t-piece or adaptor anywhere. I was checking my boot today and I smelt petrol, after pulling some foam between the fuel tank and the cockpit trim board I found a thin bore metal pipe, having read up on it I believe this is the MU return pipe. What I don’t understand is why I haven’t noticed that this pipe is hanging loose before, I’ve been driving the car for 11 months now and it hasn’t been disturbed in that time. Can anyone tell me what diameter this pipe is so I can get some appropriate hose in to connect it to the tank?

Ian

[John L]

The Moss catalogue is useful for this sort of detail, it depends whether you have a CP or a CR system.

https://www.moss-europe.co.uk/shop-by-model/triumph/tr5-6/fuel-system-induction-controls/fuel-injection/fuel-system-tr5-tr6-to-c-cp50000.html

https://www.moss-europe.co.uk/shop-by-model/triumph/tr5-6/fuel-system-induction-controls/fuel-injection/fuel-system-tr5-tr6-to-c-cp50000.html

Hope that helps

John

[iani]

Thanks John, I’m very familiar with the vendors diagrams, the trouble I have is that I have an early CP car that has been fitted with some later parts, an all too familiar situation I suspect. I have a new fuel tank coming, this is a generic model as most are now and I  have the opportunity to reconnect this MU to tank line, I’m just looking for some assistance as to how to do this, if I cut the original pipe that ran to the filter that’s fine, it is just that the bore is much larger than that of the MU line and I’d like to understand what size of reducer I need.

 

Ian

[John L]

Iani

I have a early CP system, that I would like to update a bit.

If you are getting a new tank, I would make sure it has 2 return positions on the left top side, one should be for the return of fuel from the pressure regulator valve, a decent size not to restrict any flow and the other would be for the leak back from the MU, which should only just be a dribble anyway.

If you look at the images for the CR you will see that it has 2 return connectors.

John

[iani]

21 hours ago, John L said:

Iani

I have a early CP system, that I would like to update a bit.

If you are getting a new tank, I would make sure it has 2 return positions on the left top side, one should be for the return of fuel from the pressure regulator valve, a decent size not to restrict any flow and the other would be for the leak back from the MU, which should only just be a dribble anyway.

If you look at the images for the CR you will see that it has 2 return connectors.

John

Thanks John, my car is a CP model, however it has been fitted with a later tank. Today I have realised that I have broken the MU pipe off of the pipe that used to run down to the original filter housing, it looks like this part was just used on early cars and isn't available, in any case I'm not using the original filter housing so need to try something else. I have ordered AHA5535 from Moss which I think should sort it out, I just need a flexible hose to connect them and all should be well.

[Waldi]

Hi Ian,

I have a CP model too.

return pipe from MU to tank is 3/16” OD.

Originally, the rubber connection hose pieces were not clamped, as Peter W. recently explained in another post, but he also recommends to use clamps now and that is what I already did. That would  also be better when the pipe get’s blocked and pressure rises.

Regards,

Waldi

[iani]

47 minutes ago, Waldi said:

Hi Ian,

I have a CP model too.

return pipe from MU to tank is 3/16” OD.

Originally, the rubber connection hose pieces were not clamped, as Peter W. recently explained in another post, but he also recommends to use clamps now and that is what I already did. That would  also be better when the pipe get’s blocked and pressure rises.

Regards,

Waldi

Thanks Waldi, I have a new pipe ordered and I have hose that should fit, I'll sort some clips out too.

[CP26309]

I too have an early CP (1969) many years ago when my original MU was changed the garage fitted a non standard return pipe without clamps and it popped off ...as it's directly below the Dizzy it caused an expensive engine fire! So beware!

[iani]

1 hour ago, CP26309 said:

I too have an early CP (1969) many years ago when my original MU was changed the garage fitted a non standard return pipe without clamps and it popped off ...as it's directly below the Dizzy it caused an expensive engine fire! So beware!

All sorted now, my car is CP26093 so within days of yours I expect.

Ian

[DaveN]

That ‘return’ pipe is only the cavity drain and there shouldn’t be any real pressure in there. If it should get blocked the engine will run extremely rich..... and you’ll know there’s somat amiss!

[stuart]

15 hours ago, CP26309 said:

I too have an early CP (1969) many years ago when my original MU was changed the garage fitted a non standard return pipe without clamps and it popped off ...as it's directly below the Dizzy it caused an expensive engine fire! So beware!

The return pipe on the early cars are only push on connections anyway.

Stuart.