Datsun Roadster Forum-311s.org

My old fuel tank was rotten and Tom came through with an early tank that has no return nipple. My late model carb (I think?) has a return line (as does the body).

Mechanic says that the carb will not work if the return is capped- will create too much back pressure. I thought that I read something about this a long time ago but can't find info in a search.

Solutions ? -

1) Cut panel including the old intake and outflow from the old tank and weld it to the new tank. Should work but logistically difficult.

2) Come up with a fix for the carb.

3) Use an old model carb that I have. Again, doable but the new carb is nicely rebuilt and the old carb would need a lot of work.

Thought will be greatly appreciated.

Chris

I think you can cap the return line off with no issue whatsoever Chris. There are several threads on this where late model owners have capped these lines. I'd wait for others to chime in, but should be no problem.

"Mechanic says that the carbs will not work if the return is capped- will create too much back pressure."

You might want to look for a mechanic more proficient with SU's.

There are very few real differences between early and later roadster SU's. Other than some thread differences and other tweaks to the parts, the carbs are functionally/generally the same. The very late ISO SU's had some primitive emissions provisions too, but that can be easily eliminated/non issue.

ALL the roadster fuel pumps put out about the same pressure, so that is just silly unless someone put an electric fuel pump on it. In that case you might need a pressure regulator - otherwise no.

The real benefit to the fuel re-circ system is it keeps the fuel cooler which MIGHT prevent vapor lock. All the earlier cars up to 67 did not have re-circ. and the SU's do fine.

Rather than capping off and leaving all of that junk on the carbs, just swap the fuel inlets from the old carbs to the new ones. Then you are set up like the original cars and the return line is just excess baggage.

What a great idea!