Datsun Roadster Forum-311s.org

While fine tuning the timing and adjusting SUs for the first time, I am left looking at two fuel pipettes which sans air cleaner and without being plugged could be very bad. Could not the plumbing be temporarily and safely routed from carb bowl overflow to carb bowl overflow? Or, is it a given that if the carbs are balanced, if one is overflowing , both would be. Any explanation concerning function and cause would be appreciated.

It isn't a tuning issue but a safe guard.
In the event of the floats, becoming "sinks" the float bowl must vent to the atmosphere or the fuel may end up dribbling into the intake of the engine.
The float valve can also get stuck open by debris in the fuel line getting trapped at the valve.
Make sure that the vent tubes extend ALL THE WAY down well below the exhaust system for obvious reasons.
Edit:
On your '70, the overflows probably enter the air cleaner housing but they should be operable just the same.

And keep a fire extinguisher within reaching distance or very quick access. Really should be given for all cars on the road to have a fire extinguisher somewhere.

The overflows do indeed lead to an opening to the velocity horns inside the breather.

Sorry saw this is for a late model.
I didn't know they were different.

Neither did I. That's why I didn't get it.... but your post led me to an answer. Thanks

So here is the intel on the overflow tubes. Only on the 70 SPL were the overflows routed into the back of the air cleaner assembly and further into the top of the velocity stacks. It was more a nod to federal emissions than of functionality. Earlier models had pipettes that just turned down at the top of the fuel bowl and overran down onto the frame. It is necessary to have the tubes open to atmosphere to function properly. Blocking the tubes is not an option, and they can be rerouted, but as far down and as far removed from the exhaust as possible. Overflow will not occur unless your carbs are seriously messed, but it only takes a pinhole in a float or a stuck needle to cause. All this is second hand so take it with a grain of salt. As for me, I will fix as originally designed and carry an extinguisher.....