Datsun Roadster Forum-311s.org

Anybody ever measured the amount of oil need to be added in the tops of the domes on the carbs for the little plungers? I know there are lines on the shaft but i always have trouble getting in between them. Not to mention they are kinda hard to read. I usually use the cap off the oil container to measure but have been thinking about switching to an eye dropper because I usually end up overfilling and then have to take some back out by letting a paper towel soak it up.

When I was a kid I used to fill them up a small amount and push up the piston with my fingers. I wanted a steady push, no easy spot. If I overfilled it a bit, that was OK because it would self level, and a small amount of oil in the top isn't an issue to my knowledge.

What do you mean by pushing the piston up with your fingers?

He means taking off the air cleaner assembly and pushing up on the piston within the carb inlet which is resisted by the oil.

^ Yep! It also gives a real feel for how different weight oils resist that rise, and that is part of tuning an SU. How fast that piston rises effects air/fuel ratios, especially with large throttle changes.

As the original poster said, there's a plunger with marks for high and low oil levels. However, unless a guru like Keith tells us otherwise, I believe you're fine so long as you're somewhere between those marks. I don't believe a cc or two difference will change operation or function unless it's below minimum. It would be nice to know how much oil it takes for when you have disassembled/cleaned them so you're not pouring in a bunch of oil. I don't know if there's any way for it to drain... I don't think so.

Gregs672000 wrote: Thu Sep 02, 2021 9:57 am I don't know if there's any way for it to drain... I don't think so.

Only if you end up on your lid.

Ok, this might be TMI, (Too Much Info) But my carbs have run great for years, have required little to no adjustment, and they drink whatever is in there in less than 10 minutes.
If I fill the dashpots, then go to start the car, crank over is noticeably longer while the plugs get unfounded by the ATF.
I do put some in occasionally to keep the plungers clean!

I’m not sure how that would be possible unless the oil is leaking out of the center oil well into the base of the piston.