Stromberg damper oil.

[Norton]

Hi.
-73 S3 V12. I am fiddeling with the carburettors and adjusting the needle height. But what about the damper oil? What effect will a heavier oil give? And a lighter oil? And what effect, if any will a low / high oil level give? Critically low level I have experienced and have replaced the O ring on all four.

Thanks, Harald.

[DWW]

I expect thicker oil will increase the damping therefore acceleration and deccelaration will be more gradual. I would guess the performance will be less ‘sporty’.

[Norton]

Thank you.
Have been using 20/50 engine oil, then for some reason I cannot remember I changed to straight 30. And I lowered the needles slightly at the same time. Probably a bad idea, as you should never change two parameters at the same time. Which I deep inside knew, but on the forum it seems to be agreed that its hard to tell if the the oil viscosity really matters. Anyway, now I’m gonna try 50 oil as the engine have some hesitations on accellerating at a needle position I feel is pretty much right.
H.

[DWW]

Just use SU oil available on auction site or ordinary 3 in 1 oil.

[bitsobrits]

Lowering the needle will make the mixture leaner for a given piston height. And increasing damper oil viscosity can introduce short duration lean flat spots on rapid throttle opening as the air piston lags the airflow. If you don't know what you are doing, following the factory manual exactly would be the best path forward. The factory specifies a relatively thin oil for a reason.

[DWW]

too

[Allrand]

Sorry, have to disagree. Thicker oil retards the rise of the piston, and causes temporary enrichment on rapid opening of the throttle plate, due to the higher air speed across the jet, which slows down as the piston rises and mixture returns to correct for the throttle position. It is effectively the accelerator pump.

[abowie]

causes temporary enrichment on rapid opening of the throttle plate, due to the higher air speed across

This is how I understand it.

So thicker oil or stiffer springs make the mixture richer when you open the throttle.

[Allrand]

Also stiffer springs will make the mixture rich throughout the range because the piston is kept lower. Conversely a weaker spring will weaken the mixture, it's all due to the varying venturi effect.

[malcolm]

Thicker oil, more resistance, richer mixture which is required for acceleration. I just use 20/50 and top up when I'm putting the oil in the engine anyway.