Datsun SU Carburetors

[RLJ]

What dampening fluid was used and recommended by Datsun on stock SSS engines with the Hitachi SU carburetors?

 

Was it the same for the Z cars?
 

[Stoffregen Motorsports]

Marvel Mystery Oil

[RLJ]

Thanks Matt,

 

Don’t think Marvel Mystery Oil was the factory recommended fluid. Have read where it is commonly used by people though. 
 

Just read in an L24 factory engine service manual that 20 weight motor oil was used. Noted that never use 30 weight. Wonder if it was the same recommendation for SSS engines. 
 

The dampening oil viscosity is one of the tuning tools for the SU carburetors. It can range from no oil to most any viscosity oil.

 

 

[MikeRL411]

I used Singer sewing machine or 3 in 1 oil and they work ideally for me!

[Stoffregen Motorsports]

The dashpot dampers in the SUs on our race car are cut out completely. No springs either.

 

Street engines and mild stock class racing engines respond well to the thinner Marvel Mystery Oil. Though some filing of the needles may also need to be done to get the optimal tune.

[wayno]

I use power steering fluid in my LZ23 engines and my Roadster U20 engine.

[datzenmike]

The damper oil thickness acts like an accelerator pump to slow the sudden opening of the piston or slide causing a bog. Thicker viscosity richer and thinner leaner. I've heard three-in-one and I've heard ATF.

[RLJ]

Power steering fluid is pretty much ATF.  I used ATF with some 20 weight fork oil mixed. 
 

Started with nothing, way to lean. Went to Marvel Mystery Oil, better but still to lean. Went to ATF, better still but still a little hesitation of idle. Mixed some 20 weight fork oil and throttle response and drivability is good. 
 

Observations. The more modified the engine is with longer duration cam and less manifold vacuum at idle, the thinner the fluid all the way to no fluid. 
The more stock the engine with higher manifold vacuum at idle,  the thicker the fluid. 
 

 

 

[Stoffregen Motorsports]

You could also play with the height of the needle in the dashpot.