For better or worse, I take oils seriously, as it has been my life for the last couple of decades. If you look at what SU says on their site:

"The first is SU Damper Oil, which is a straight 20 grade and comes in a handy 125ml bottle. This oil is for use where the carburetter is fitted with a damper inside the piston and can be used on all SU, Zenith and CD carburetters.

SU Damper Oil (125ml), Part No: BDR125S"

That means at 40ºC, it will be the same as a 5W-20 or 0W-20, but at higher temperatures it will be more like a 5W-30. Because it is in the air stream, I doubt that it gets very hot.  (I have an SPI, and there isn't a good way to shoot the laser under the big filter to measure temp). So I would consider the 40ºC part of the spec, which would be using the 5W-20.

So if you are going to play with the "right" viscosity for your carb, in your use, I would suggest these two as starting points if you don't want to buy the SAE 20 product that is sold by our host.

A SAE 20 would be about 50 to 60 cSt at 40ºC. ATF is about 34 cSt. Fork oil is about 18 cSt. 20W-50 is about 170 cSt.

I would think that 20W-50 would be way too thick, and ATF is way too thin. Motorcycle fork oil is half the viscosity of ATF (and way more expensive), so that would also be off the table in my opinion.

It's been 52 years since I had my last SU carbs, and I don't remember what I did. (Bugeye Sprite). I know when I had them balanced and running right, it got 54 mpg, so I probably did something right. (DC to NY on $1.05 in Gas)(and $3.95 tolls).

Derwood,

I know im a little late on this one but you wanted to know what types of oil people are using so here it is:

I personally have tried all the oils that people have mentioned in this thread and finally settled on Amsoil 20W synthetic compressor oil.

https://www.amsoil.com/shop/by-product/compressor-oil/synthetic-compressor-oil-iso-46-sae-20/?code=PCIQT-EA

I found that it works best for me during all-season driving.  I had performance issues with 20W-50 during the cold season and have been very satisfied with the straight 20W.  Currently running a 1380 engine with single HIF44, yellow spring and BEU needle.

Let me know if you have any questions.

John

Although I've not done the experiment, the Mini engine tells you when the oil is low by providing lousy throttle response, resulting from dashpot over-reaction. As the oil gets lower, the hesitation becomes more pronounced.Try it again Doug,  but open the throttle very slowly - the spring will produce the right air-fuel ratio.
Lee Valley Tools used to sell large syringes complete with needles for shop work, 5-pack if I recall. The one I use for carb oil has the needle point cut off square to avoid getting (more) oil in my veins. The plastic syringe isn't very resistant to oil, though.

I agree.. no need for a syringe. Just remove the bell and tip out the oil .... if you ever need to get rid of it.  

And... be careful with the cleaning.  Use a solvent (gas?) only; the piston and the outer bell work very closely together ..you do not want to use a scourer or anything harsh that might damage the inner surface of the bell or affect the clearance between the piston and bell.

Cheers, Ian

Great advice that I will certainly take. Thanks Malcolm !

The countdown is on, and I’m getting excited to soon have my Mini. Considering that I’ve wanted one since owning the rusty mk2 , which was 38 years ago, and considering that I paid the money for my Mini about 5 weeks ago, I feel pretty freakin’ good :-)

I received an email from the driver today.The car has only moved to the transport companies Edmonton depot, but he told me that he is starting to head my way from Edmonton on Friday, and he will be sending me a tracking number at that time. So I believe he will likely be on time as scheduled, with delivery here in Charlottetown on March 3rd. What a day that will be for me....

Cheers and thanks for the tip ! Darren.

Just take the dash pot off it only has three screws and clean it up inside while you have it apart.

Derwood,
I doubt than anyone other than me has done that experiment. Have at it.
Just remember to put the oil back in afterwards

Well gents, this has been a thorough and interesting debate. Actually quite a bit like the blog that spurred me to start this thread. But I certainly learned some things that will help me out, so thank you all for your contributions. I intend to buy a small syringe whenever I spot one that is suitable for drawing the dashpot oil out. Cheers all ! Darren

PS- no fear of me running out of questions anytime soon. As I find the answer to one question, I will likely already have something else that I wish to better understand. Zoom zoom.

Neat.  I knew it was an old product.  I've seen some pretty old tins of the stuff.

DLawson. some history behind..  3 in 1 oil.. it came out in 1894   George Cole in NJ.. invented / formulated it use on Bicycles..  later b c

The answer is"no" to both questions. The spring is necessary; otherwise the dashpot piston would rise too far for a given rpm, then fall again because the level of vacuum between the bridge and the throttle would drop too far, then it would probably do this over and over again. Think of the dashpot piston as a valve that meters both fuel and air at the same time. The spring is carefully calibrated and is amazingly long for the size of the space it sits in. You would not be able to stretch it without deforming it and it would rub somewhere and not function properly. It is high-quality metal protected from the elements and is under light loading, so it won't corrode or weaken over quite a long time.
Here is a photo of the two dashpot springs I mentioned in my post and a (fuzzy) picture of one beside a HIF44 carb.

I've always had great results using ATF oil in my mini

3-in-1 Oil
Blue/white bottle = 20W
Black/white bottle = 30W

derwood. I always just used  3  in 1 oil that comes in the small can for about $2.. think it is about 10W..and never had a problem with the 500 plus minis/mokes  I have imported in last 22 years.. later bc

Stop teasing Derwood - he has to wait at least 2 weeks before he can try it.

Yes, there is an internet troll here, PURPOSEFULLY and REPEATEDLY giving bad information. 

Derwood, go back and look at what I already posted -

"Take this to the ludicrous degree to understand it. If you had NO carb oil ( very thin!) the piston would fly up, the needle would reach minimum diameter and you would think maximum richness. Nope, the engine would die. Leaned out."

go try it.
Take a small insulin needle/syringe, suck out all the oil out of the carb damper, and see what happens. You will stall. Without oil, piston flies up too quickly, creates a wide-open venturi/choke area, airflow is thus much too slow for that rpm, so there is not enough speed of airflow to create enough suction to draw enough fuel at ANY needle position. This is physics - read Bernoulli's principle.

Actually, Specialist is "WRONG AGAIN". The operation is opposite to what he says.

With the throttle closed, there is high vacuum in the intake manifl
old but not in the carb. As the throttle opens, vacuum is applied to the carb, especially between the throttle plate and the venturi (the gap between the bridge and the bottom of the dashpot piston). In that space is a port leading to the dashpot chamber. The vacuum PULLS the dashpot up, making the venturi gap wider and allowing more air in. At the same time, the main metering needle is also being pulled out to let more fuel in. The needle is chosen and tuned to provide the right mixture at any position of the dashpot piston. At any steady throttle position, the dashpot settles with an equilibrium between the vacuum in it and in the space between the throttle plate and the venturi - the dashpot spring determines that.
The trouble occurs when you open the throttle quickly. This applies high vacuum to the carb and the dashpot, causing the piston to rise too quickly and tesulting in a momentary LEAN condition because the air flowing past the top of the main jet isn't moving fast enough to pull enough fuel out to suit the large venturi opening - the engine isn't turning fast enough to keep the air moving fast enough for the right mixture, and the engine stumbles. (Application of some choke will compensate this,)
The dashpot damper slows the rate of rise of the piston, which limits the volume of air passing through the venturi gap, so it tries to flow faster across the top of the main jet and more fuel is pulled out, producing a momentary slightly rich condition during the change in throttle opening. On fixed venturi carbs, a small accelerator pump is needed to do the same thing.

On a car with a fixed venturi carb, you can 'pump the gas' while trying to start it, but on a SU carb, you're wasting your time because there is no pump.