Oil in the 2” sandcast carbd

Just to check: are these to be filled with oil in the central tube, as the normal SUs?

yes they are filled like the others

Thanks. This forum is so good!

as with all the SU, …the correct SU carb oil oil is helpful to the carb performance. Penrite, SU are specifically made for it. Nick

Which Penrite?
I use ATF which is about as thin as SAE 20 oil

Hej Peder,

So do I. And the viscosity of ATF is less temperature sensitive and thus will keep the mixture more stable!!

Bob K.

SU/Zenith SU oil is made for…well…SU carbs…the tuning of SU carbs as from SU is based on that oil type, of course other can be used, if similar, but why? SU formulates it for SU.
ATF is similar enough, possibly a bit too thin, so is straight 20W synthetic engine oil, but don’t use multi-grade as some have recommended (hoping I suppose that at a certain temp it becomes just right, well how bout all the other temps?). Synthetic, in a single grade, is less affected by temperature changes.What the oil does is control the rate of the piston movement. Watch for any hesitation on quick throttle. Often someone that experiences that hesitation…fiddles with a lot of tuning…when it is the dashpot oil. One comment was: if the dashpot oil is too thin, there will be insufficient damping of the piston on acceleration, and the piston will rise too far too soon, which decreases the vacuum at the bridge (that is, at the jet and needle) which decreases the fuel coming through the jet, resulting in a lean mixture and hesitation on acceleration. From Moss motors: IF …too lean a mixture on acceleration, try a slightly heavier oil; if too rich, then a lighter oil is indicated. Some feel the SU/Zenith is costly. SU brand comes in a small 125ml bottle for as low as $14 (Moss) --to about $18… and will probably last a year or more. A tiny bit weeps past the piston…as it is supposed to…thus the periodic top up…if you overfill , when you push in the damper lid and screw in it will push a bit more thru…no worries after a few minutes of engine running. Nick