"natural" fuel level (without fuel pump) on my TR4A SU carbs

[Z320]

Hi,

this is something I noticed years ago:

with the petrol tank of my TR4A topped up I have fuel pressure on the SU HS6 carbs.

I also noticed  loss of petrol during winter while the car was stored with full petrol tank - in my opinion by vaporisation in the float chambers and slightly leaking ball valves?

Today I had some time to make a measurement on the front carb, first with 30 l fuel the level was about 48 mm below the ball valve / rim of the float chamber.

Second with 40 liter fuel the level was about the height of the ball valve.

Last test with 50 liter fuel (max 52 liter) the level was abot 50 mm above the ball valve.

Because the TR-engines are angled in the frame some degrees the level on the rear carb is slightly higher related to the float chamber.

So on the rear carb the „natural“ fuel pressure with 52 liter fuel in the tank is max about 70 mm.

This is less then I remembered, but anyway remarkable. This info may be useful in any discussion.

Ciao, Marco

Edited August 26, 2023 by Z320

[RobH]

Maybe it's important to turn the fuel tap off then, if the car is left for some time with a full tank. That will prevent syphoning. 

[Z320]

The TR4A has no fuel tap,

I added one because this can be useful in the case the fuel pump has to be changend.

But I never closed it for storing the car - next winter I will do this.

 

[Michel Higuet]

After the winter I always need to fill to float bowl, there is no more fuel in it, everything is slowly evaporated during the winter. 

[Ralph Whitaker]

I have an electronic fuel shut off valve fitted which cuts off the fuel supply when the ignition is turned off. It has a by-pass tap built into it in case of failure, but been OK so far and it has been on there for three years. Makes working on the fuel system simple and stops syphoning. Keep meaning to put a hidden switch in the circuit too as an anti theft measure but not got around to it yet.  Doesn`t stop the fuel in the float bowls evapourating away though as they are open to air via the overflows.

Ralph