Datsun Roadster Forum-311s.org

Greg, thanks for the great advice. No gas in the float. blew, valve works perfectly. May have had something in it. Before I start it up again, I had a question on the oil in the carb. How do I know if there is enough oil in it?

Gregs672000 wrote: Sun Aug 07, 2022 12:11 am The carbs can leak around the brass washers that connect fuel feeds too. I would consider replacing the old floats with the plastic ones as the brass will eventually sink I hear., unless their stupid expensive (never priced them).

+1...on this recommendation. I really did have a Nissan, new out of the box, brass float fail, (gas gets inside the float) after less than 500 miles...I'm not kidding....I was shocked

I was finally compelled to order the plastic ones, after the price had doubled, from when I first read, on 311s, years earlier that it was a good idea to replace the brass ones....just say "YES"....just do it...and then forget about that issue..IMHO, of course..
Mike

garcia_vm wrote: Mon Aug 08, 2022 3:32 pm Greg, thanks for the great advice. No gas in the float. blew, valve works perfectly. May have had something in it. Before I start it up again, I had a question on the oil in the carb. How do I know if there is enough oil in it?

Glad to help. Yes, things can get stuck and keep the valve open.

Regarding the oil, typically, there are marks on the plunger, but mainly the idea is that it has enough to control the movement of the carb piston when it rises up. If it has too much it will "self level" so that speak, not enough and it may not work right (?). The function of the oil is to slow the rise of the piston down so the carb does not suddenly lean out when you open the throttle. People "tune" their carbs via different weight oils... I'm not an SU expert, so if you need advice on what oil to run you may need to ask someone like Keith. I have used marvel mystery oil, AFT and light motor oils, but that was 30 years ago!

So many household uses … and just happens to match the OEM 20W dashpot oil recommendation - Works like a charm.
(Not brand specific - Any 3 in 1 oil will work)

thanks for the oil info

Mike, Greg
I think I do want to upgrade the float.
I went to datsumparts.com and they have parts for R16 & U20
How do I know what carb I have?
Under R16 only SKU:1628
Under U20, both SKU: 1628 & 1629
which do i buy?

Jon posted the link to the correct one earlier: 1628

Bwk2000 wrote: Tue Aug 09, 2022 9:30 am Jon posted the link to the correct one earlier: 1628

Yes...that's what I ordered,...Dean's SKU 1628... and still using on my R20 stroker with the original R16 carbs........

Just wanted to say thanks.
Looks like blowing into it cleaned it out. No gas flowing out anymore and the car sounds good.
looks like i have a lot to learn, looking forward to it.
Thanks again
Victor

We're here to help! Welcome to the family!

Hey guy I think I might also have a fuel overflow problem as I drove it a little while ago, I'm not sure if I smelled gas or just the exhaust but when I saw y'all talking about cut overflow lines I looked at mine and just wanted to make sure I'm looking at the right thing as this is my first car with carbs. If y'all could just lmk if that cut tube is the right one or if I'm looking at something else? And also if anyone has a link to buying some new ones?

Respectfully,
Kinnaird

Yup. That’s the one … or two if they hacked the other one up that badly.

You can use any 1/4” hose (I prefer clear) and run it down exiting to the outside of the frame and towards the road (keeping it away from heat sources). I would also use clamps on yours since the tube was cut so short.

P.S. Welcome!

Bwk2000 wrote: Fri Aug 19, 2022 5:48 pm Yup. That’s the one … or two if they hacked the other one up that badly.

You can use any 1/4” hose (I prefer clear) and run it down exiting to the outside of the frame and towards the road (keeping it away from heat sources). I would also use clamps on yours since the tube was cut so short.

P.S. Welcome!

Thank you! I'm just beginning to diagnose some problems and I'm taking it to a shop to just do some routine stuff and make sure it's all safe before I start learning on it haha. I'm glad I came across this thread so I can try to solve that problem beforehand.

Thank you for the welcome, I'm excited to learn some more mechanics and how to manage the stress that I know it'll bring haha.

Bwk2000, if I were you I would remove what is left of the tubes and braze in a new length, bent at 90deg.
You could do the entire tube in rigid line, curved as required or securely fasten some rubber tube to the bend to do the job.
The factory overflows went right down the side of the engine and were held there by two little brackets which were clamped under two sump fasteners.


Front view gives a good idea of the two overflow tubes.



They were available new at one stage but this image is decades old

Nissanman - Yup - It is on my list. Been trying to find good original ones, but no luck yet. Could fabricate a couple brass (or even copper) tubes to put on there, but I would just end up tossing them once I (eventually) find good OEM ones. So, that’s why the 1/4” clear plastic tubes are there. They work well and will do until that day comes when the right parts find me

As said, yes that is the fuel overflow. Now, how often do these carbs in general tend to overflow? (I have not messed with SUs in many years, but I don't recall mine overflowing ever on the L-20 I had in my 620 PU). I'm thinking there may still be some needle and seat issues in the float bowls, or something that's occasionally fouling the needle and seat so it doesn't seal? So yes, do fix the piping, but maybe there's still some additional exploration required to solve the whole issue unless the carbs naturally tend to overflow from time to time...?