What type of oil should be used?
Too often people use light duty (sewing machine or general purpose) oil in the dash pot assembly. This type of oil does little if anything to impede the upward movement of the piston as the throttle opens.
Engine oil can be too viscous (depending on climate). After 2 hours of driving it ends up in the bottom of the piston, the majority of it sucked into the engine. This happens because it is too thick to pass through the damper as the piston falls causing the oil to flow out of the top of the dashpot.
I use a mix of 20W-30 to 20W-50 and sewing machine oil. The ratio is three parts engine oil to one part sewing machine oil.
When you use the aforementioned oil mix if you attempt to raise the piston when the engine is cold you will find that a lot of force is required to move the piston to its uppermost position. When you release the piston, it will drop to the bridge quickly (less than half a second).
Fuel System Description
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Covers Stromberg 175 CD-2 SE and SU-HS 6 Carburettors