Datsun Roadster Forum-311s.org

The carb closest to the cabin has a tube that drops down under the engine:



The carb closest to the front of the car looks to have had its tube cut off:



What is that tube? I've been trying to go through the service manual from the wiki but it's not clear to me what the tube is.

Should/Can I do anything?

Overflow tube, normally no fuel should be coming out of it. Ideally the tube should be long enough to exit fuel down toward the ground. Fire hazard if it should flow over the exhaust system or other ign sources.

They both, as suggested, should extend to just below the junction of the sump and engine block to vent any fuel overflow from dripping onto a hot exhaust.
A matter of urgency to rectify

Nissanman wrote: Tue Aug 08, 2023 3:48 am They both, as suggested, should extend to just below the junction of the sump and engine block to vent any fuel overflow from dripping onto a hot exhaust.
A matter of urgency to rectify

Dang... Glad one of the first things I bought after getting the car is a fire extinguisher.

Any suggestions on strategies for rectifying? Can I buy a fuel hose and clamp it on, or is the temperature too high on that part?

Short term, yes a fuel hose can be used, just route it well clear of any hot bits.
To renew the original vent pipe will require drilling out the old stub, brazing in a new length of appropriate sized bundy tube, shaping it to suit the path down the engine and inserting the tip through the small bracket that SHOULD be under one of the sump retaining fasteners.
What the OEM O/flow tubes look like.

Where the factory pipes are located on the SP310 1500.

Tabs that the O/flow tubes pass through at the sump.

Really appreciate all the info, and especially the pics, Nissanman!

I bought two feet of fuel hose, attached it with a cable tie, and routed it down away from the engine. I’ll keep my eye on it and figure out a long term plan to get it fixed properly.

Yep, doesn't have to be factory as long as you route the tubes/hose away from the exhaust. These don't overflow often. Someone may be remanufacturing them (?).

The '64 I bought had both overflow tubes cut off. I had some spare brake line and bent it to route to below engine as shown in the picture. I used a short piece of fuel line to splice the lines together.
One of my floats sunk and the overflow tube worked just fine.

The early cars (pre 67.5 iirc) had the long tubes which if you had the grommet fail or the brackets missing would crack and break from vibration. Later ones were much shorter and had some tubing stuck onto them to run it away from the exhaust.