Hey there people,

There seems to be a lot of different ideas about this - consider the single SU carby.

What oil should be used in the piston assembly where the piston damper screws into the top of the suction chamber?

Light oil such as sewing machine oil, another person told me to use automatic transmission fluid which is what I am using at the moment.

What do our Ausmini members use in their cars

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Rod
http://smg.photobucket.com/albums/v607/Rodney/

Mini clinic told me to put normal synthetic
engine oil in there cos it copes better in the heat.
used it on mine and never had a prob

Use the oil that make it go the best with out any flatspots. I have used Auto tranny fluid to dif oil to try the different effects. Auto tranny is usually goo but motor oil like SAE 30 is what I have found to work the best for me

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I've Got One
You've Got One
We've All Got One
What Is It



A Bloody Mini

1970 Mini K, 1380cc, 1.75 HIF SU, 30 70 Cam, 2" Zorts
1969 Mini K, Stock Standard and Orginal. (Slow as Hell)

this is one of the mystical sciences....

the weight of the oil required depends entirely on the way the car drives... it's not something that can be worked out on a dyno, and not something that you can be told "this is the right one for you", you've gotta drive the car around corners, and accelerate out of them - if the oil is too light you get a dead spot under acceleration - explanation below. ATF is a good middle ground between way too light, and too heavy. With a ported head, I used to run ATF mixed with 25W engine oil. The ATF was too light, the engine oil too heavy. In most cases, sewing machine oil is way too light. Now with a more standard head I'm using "official" SU carb oil - it's much lighter, and now that I think about it, I think it's too light - must do something about that... my needles are too rich down low also, which adds more confusion

First thing to understand is what the oil does - it stops the piston in the carb from rising too fast - it's a dampener - if the oil is light, the piston rises fast, if it's heavy, it rises slow.

Next, why does the piston rise? the air getting sucked through the carb pushes it out of the way when the throttle opens.

Next, what happens when the piston rises? fuel gets sucked out of the jet by the air passing over it, mixed with the fuel and exploded in the cylinder

What happens when the piston rises too fast? if the piston rises faster than necessary, then the air passing over the jet won't have enough velocity to suck out the required amount of fuel - you get a lean mixture until the air speed picks up enough to suck up enough fuel to get the mixture right for full potential.

Empty the dashpot and go for a drive - plant your foot on the accelerator from low revs and your car will gasp, no power and no performance, revs will slowly rise until it suddenly takes off - I did this with my 1310 and twin 1 1/2"s and I had bags of wheelspin in 3rd gear as it suddenly got the right mixture. Play with the oils until you don't get a gasping flat spot on wide open throttle acceleration, but it doesn't bog down either

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I'm currently using atf , it's a little too thin and I have a small flat spot when going from a standing start so when I get around to it I'll be changing to a 50/50 mix with 20W engine oil.

I use a dellorto, this solves the SU mystical art dead in it's tracks sorry had to say it

I did use Castrol light machine oil that was SAE20 in my 1 1/4 SU and it seemed to work well for me. SAE50 was too thick, the throttle response was lethargic at best.

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Lillee - 1969 Morris Mini K

The latest for me that seems to work really well is the lubricating oil use for air tools. It was the only thing i had available at the time, but it seems to work as well if not better than anything else i have used.

Cheers
Aaron

Ooops - forgot to mention that when I go around a corner, I sometimes get that second or two when it seems like fuel starvation, then she kicks in and away we go again.

That would be that flat spot you mention above.

Think I'll try something like SAE 20 or 30.

Thanks for the replies everybody - the next ones will probably use different oil

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Rod
http://smg.photobucket.com/albums/v607/Rodney/

Nope thats common for all SUs... its their stupid fuel float design.... all the fuel goes to one side and hence the lack of revs from no fuel.

after months of hard starting with engine oil in the su
aaron, stevenmikey and darren told me sewing machine oil (thin white oil, a little thinner than olive oil)
would make starts easier and softer idling
and it has worked ever since
all you need in the morning
is to lift up the bonnet, jiggle the piston and it starts well after it

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forever chasing clearer skies...

Hey Yea Big willy,

I remember one mechanic telling me that - said to take the car in and he could fix the "going round corners hassle" just by adjusting the float.

Haven't done so yet but when I do I'll let everybody know what happens.

Cheers everybody 4 your responses.

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Rod
http://smg.photobucket.com/albums/v607/Rodney/

when setting the float level the fuel should "puddle" just under the top of the jet.

Going around corners under anything but huge speeds won't make it starve, it's more likely to be the dashpot oil. You think about the bowl - the hole is right at the bottom and in the middle, and it's supposed to be full of fuel - I reckon it'd take a lot of centrifugal force to get the fuel to be all away from the hole, and it'd also only cause an issue on left-hand corners - you'd get the opposite on right-hand, theoretically it'd go rich

just my 2 cents (again)

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did I tell you that I won a trophy?

I'm wondering what Mobil Jet Oil 2 (synthetic) would be like in the dashpot??? Apart from the fact that it causes nervous defects and can cause massive CNS shutdown, It'd be about the perfect weight. Ah well.............

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"He's always been a dickhead, He always is a dickhead, He will always be a dickhead. So stop complaining when he acts like one."

Think about holding a cup of whatever going around a corner. The liquid does go up the side quite a lot... so i can see how it would work the same in a SU. Food for thought