europa s2 1969, the "T "after gas pump ??

[mike alain]

Folks,   why does lotus have the   T gas line going back to the tank(at fuel tank gauge)  is this for vapor lock? or reduce pressure at carb?  I am going to run
new metal lines along frame  from/to   gas tank,  looks cleaner, and my plastic lines are  50 years old anyways.  but If I do not need this line I will just
forget about this  T that is just after the fuel pump on motor.  thanks  Mike.

[Sandyman]

Mike, the T is to dump extra fuel back into the no pressure area. To avoid fuel starvation in the carb the pump delivers more fuel than the carb needs. Best to utilize this feature when replacing fuel lines.
Sandy

[jbcollier]

Diaphragm pumps have a set output pressure set by the spring that applies the motion from the moving lever/plunger.  Once this pressure is reached, the pump stops delivering fuel until the pressure lowers again.  On very economical engines, there isn't much actual fuel flow.  This means the fuel just sits there.  At best, it only moves slowly through the line.  The wedge head has the exhaust right under the intake so heat soak is a very real problem.  In order to keep the fuel from overheating and boiling, Renault fit either a "T" with a small bypass, or a bypass outlet right in the pump.  This keeps the fuel circulating and cool which greatly reduces the likelihood of vapour locking while you are running, especially in slow traffic on a hot day.

[Sandyman]

So John, keep or delete?

[jbcollier]

On a wedge engine definitely keep the bypass.

[BobW]

It's worth mentioning that the replacement aluminum tanks available from at least one source do not have a fitting for the fuel return line. At least mine does not.

[Sandyman]

Mine from RD lacks return port as well. I think I suffered from vapor lock once. Though it was the 50 year old fuel pump. I will replace the pump and try to figure out how to route the return line.
Sandy

[jbcollier]

Something like one of these:



https://sullivanproducts.com/product/s476/

Can be easily added to tank.

[Sandyman]

Thanks John, again your knowledge is thankfully received.

[Gary t]

Easy to install? Doable but I wouldn't want to unless the tank was on my bench so I could recover the first ten dropped nuts. 😁

[Sandyman]

Gary, I am with you about dropping parts into tank. I am thinking of using some fishing line through the fitting to feed the nut onto the fitting with out loosing it.
Sandy

[GavinT]

I think the presumption here is that you only need to remove the tank sender plate.
Do these replacement tanks not have a removable sender arrangement?

[BobW]

There's a removable sender plate on the front of the tank. It looks as if there's room to drill it for a return line but I would not want to try removing the plate with the tank in place.

[jbcollier]

Usually the easiest place to put this type of fitting with the tank in place is the filler neck.

[GavinT]

My thinking was that if you drill a hole with the tank in place, where ever that hole might be, there's going to be drill swarf in the tank.
Ally swarf can't be conveniently picked up with a magnet and the bits might be big enough to initiate clogging the outlet.
Also, there's no issue of dropped nuts with the sender plate on the bench.

Just something to consider.