12 replies to this topic

[pr3nna88]

hello, could anyone tell me the correct oil to have in my dashpot?
and weather it makes any difference in what carb it is?
and ive also heard that the weather affects what oil due to its viscosity?

i have a 998, with a single hs4 carb and a stage one kit, by the way

cheers

[[email protected]]

http://www.minispare...ty=pb&pid=37250 is the correct stuff, but many people get away with 3 in ones etc.

[bunch1980]

I swear haynes says to use engine oil, thats in engine mine being 20w 50 (dont have haynes here to check at mo)
but is that maybe to thick then?

[surfblue63]

Also avaliable direct from SU Burlen

http://www.sucarb.co...l.aspx?id=26524

The grade is SAE20 so any oil of this spec would be OK.

[MRA]

Multigrades give different results as the temperature changes not good

[pr3nna88]

yeh my local car shop said use 20/50 engine oil. runs like a bag of spanners as its like glue when cold.
haynes says:

'multigrade engine oil, viscosity sae10w/30 to 15w/40, to api SG/CD (duckahms QXR premium petrol engine oil, or duckhams hypergrade petrol engine oil'

does 3 in 1 fall under one of those catagories? as i have a little pot of that and i have no clue to be honest.

whats multigrade oil? like 20/50 where as non multigrade would just be 20?

[madmike]

yeh my local car shop said use 20/50 engine oil. runs like a bag of spanners as its like glue when cold.
haynes says:

'multigrade engine oil, viscosity sae10w/30 to 15w/40, to api SG/CD (duckahms QXR premium petrol engine oil, or duckhams hypergrade petrol engine oil'

does 3 in 1 fall under one of those catagories? as i have a little pot of that and i have no clue to be honest.

whats multigrade oil? like 20/50 where as non multigrade would just be 20?

not sure what multigrade it is but i use 3 in 1 and it works fine with no problems.

[surfblue63]

As SU Burlen sell SAE20 for putting in the dash pot I would go for that. Other oils may work, but with multigrades they can change viscocity, and thus the amount of damping.

[bunch1980]

Right so if i buy su oil form minisparses how will i get old out? a syringe maybe? lol

[pr3nna88]

Right so if i buy su oil form minisparses how will i get old out? a syringe maybe? lol

i did this yesterday.

if you unscrew the dashpot screws while keeping the dashpot in positio it is possible to lift the dashpot piston and needle out in 1 which means the oil doesnt go everywhere (a little bit did when i did it) then clean it out and put it all back together and fill with the correct oil.


i think im gonna use 3 in 1 as i already have some of that and ill add the su oil to my next minispares order

[TopCatCustom]

In theory you should use different oil depending on how rich/lean your engine is under throttle, thats one of the downsides to carburettors- any temperature, humidity, atmospheric changes all effect how your carb performs so from day to day with weather changes it is very rare that a carb is ever in perfect tune.

Thicker oil will make the engine lean out under acceleration as when you open the throttle, velocity through the carb increases but the thick oil stops the piston lifting quickly so the needle limits fuel mixture, thinner oil means the piston lifts faster under acceleration meaning it will be richer.

Of course a rolling road session will sort this out to "near enough", either changing the oil viscosity or needle to get the fuel mixture right. But dont forget- if you change anything with a carb it will want setting up again

[bunch1980]

Thanks for the tips, I guess can only try changing and see how it performs or not. Im sure its long due a rolling road tune up to, something i plan to have done in new year to.

[andydclements]

Thinking as I go here, so.

So, 20 SAE is the correct oil.
20w50 (multi-grade) would be the same viscosity as 20 SAE at the hotter temperature point.
20w50 would be the same viscosity as 50 SAE at the cooler temperature point.

The carbs do not get to the same working temperature as the main body of the engine, I guess when in warm weather the carb gets to 10 degrees above air temp, that's well below the upper temp point of multi-grades, closer tot he lower one.
So a 20w50 in the dash-pot would normally behave like a straight 50 oil.


Based on that, and info from those that know what the viscosity of the oil does to fuel mixture, I'm going with a straight oil of 20 or a multi-grade that's a lot thinner than 20w50 (maybe a 0w30).

Thanks, I had been wondering about this for a while.