Datsun Roadster Forum-311s.org

Hi folks!
My rear overflow was puking gas after a short vigorous drive this week. I did some research here and YT and then cleaned and checked out both float chambers, needle valves, floats etc. Other than cleaning out some fine rust? Particles in the bottom of the bowl it all looks good except when I blew on the overflow fitting the rear one only blows out, so I thought it has a check valve. The other one blows freely both directions. Can anyone tell me which is correct? I could not find this anywhere?
Also, One needle was a two part assembly with a spring in it and the other was a solid rod with what looked like a rubber tip ( it was black on the conical tip). Thanks!

I had a rubber tipped fuel valve once that was worn so that it was not sealing and shutting off the gas——->overflow. Other valves I have had were metal tipped. I believe they all should have springs.
Our corn gas gums them up regularly.....
Another time I had a semi sinker brass float——->overflow.
Also some metal screens over the carb banjo bolts can decide to break and deposits bits of metal in the valves.
New valves and plastic floats might be in your future

Linda

Linda wrote: Sat May 09, 2020 4:08 pm I had a rubber tipped fuel valve once that was worn so that it was not sealing and shutting off the gas——->overflow. Other valves I have had were metal tipped. I believe they all should have springs.
Our corn gas gums them up regularly.....
Another time I had a semi sinker brass float——->overflow.
New valves and plastic floats might be in your future

Linda

Hi Linda, my floats look good, for some reason I can't upload the pic. Both needle valves passed the blow test. It's the differences in the overflows that gets me. Should they have a one way valve or be just open?

Here’s the pics
The overflow is on the right

Looks like you have the plastic floats, great.
Your overflow needs a hose on it so the gas runs down past the exhaust, should it dump gas. I believe they are open, no valve.
Do the valves move smoothly?
Is the float tab set correctly?
Make sure your choke is not stuck too while you are there.

Linda

ThankYou Linda!

The "blow test" is not an accurate assessment of the needle valve. If it continues to give you problems then consider replacement.

I chased down the same problem last year.
Replaced the float with the plastic ones you have installed, and also had to replace the fuel float valves.
Tried several new aftermarket ones which I found to be prone to failure, so I installed oem nissan valves and that did the trick.

Cheers
Ray B.

I seem to recall reading that even the plastic floats can have their problems, mainly that with age, or corn gas, or both, they can swell up and restrict their movement. So if your floats are very old it is good to check them.

Linda

I have some new in the wrapping genuine Nissan float valves available. Price is $42 each.

Stan
standatsun@gmail.com

Gregs672000 wrote: Sat May 09, 2020 8:44 pm The "blow test" is not an accurate assessment of the needle valve. If it continues to give you problems then consider replacement.

Thanks Everyone
Greg- Do you agree with Linda that the over-flow fitting on the top of the float bowl lid does not have a check valve? The bowl that over flowed was the one that seems to have a check valve - I could only make air go out from the bowl side. The other ( front float bowl) air would go either direction through it.
After cleaning them out and trying to adjust the FA mixture in the carbs ( it does not idle smoothly at 650+- RPM) I took a spin around town and did not have a overflow issue.
Top off, Significant other next to me and the dog in back- it was still a beautiful day!

I recently took 6 older carbs apart and not one had a check valve in the overflow. There would be no reason for one to be there. If the float and needle valve are working correctly there should not be any fuel there, If you do have fuel in the overflow it needs to routed down and away from the manifold. On my car I bought new banjo bolts and solderable fittings and used copper nickle tubing to route any overflow down under the frame. Some just use rubber hose to do the same.
Any time you get to go out and drive these cars is a beautiful day and having the significant other along makes it even better.

Did you check the banjo bolt screens? Debris in there can impede the fuel valves..Probably what the “ rust” was that you cleaned out of the bowls. Worth taking the whole valve out with a socket and blasting it with carb cleaner.
How are the tiny fuel bowl hoses, check for stiffness and cracks.
I would not drive anywhere without those overflow hoses or copper tubing. Risk of a fire.
Linda

Thanks Mike and Linda- I have fuel line tubes attached to the overflows and routed down under frame. 5# fire extinguisher behind seat. I guess I'm going to try to take the nut off the top of the overflow to see why it's not open to atmosphere.

Alright,I feel better that you have a hose on the overflow and a fire extinguisher in the car.
You don’t want to be the “Fire Marshall Bill“ of the Roadster world
Linda