SU HD-8 Carb Piston Spring Length ?

[Guitarstar]

Can anyone tell me what the free length should be of the large carb piston springs ? I'd like to get a feel whether some PO has stretched the springs. It would be nice to know the wire diameter as well.

I remember reading somewhere that you can measure the compressed height by putting them in a clear tube and adding a weight on top, but I can't find the data for the weight, or the value for the compressed height, and my springs no longer have any paint on them
indicating if they are even the correct type.

Thanks for any insight.

 

[Guitarstar]

Re: SU HD-8 Carb Piston Length ?

Oop's that should read SU HD-8 Carb Piston "Spring" Length ?

 

[Radford]

Re: SU HD-8 Carb Piston Length ?

XIV. PISTON SPRINGS -SU CARBS

A piston spring combined with the weight of the aluminum piston provides the necessary downward force to maintain essentially a constant pressure loss (depression) at the throat of the carburetor. The springs are initially color coded with paint for identification. The paint disappears with time. Common piston springs are as follows:


Code Force in Oz. @ Height

Blue 2 1/2 2 5/8"

Red 4 1/2 2 5/8"

Yellow 8 2 3/4"

Green 12 3"

Red & Green 11 1/4 3 7/8"


It is difficult to identify springs visually since ones with the same load rating may have different free lengths, different wire diameter, and different number of coils. The springs may also sag slightly with age and use. To identify and check for proper specification I have made cylindrical weights from aluminum bar stock corresponding to the above table. I put the spring in a glass tube with the correct weight on top of it and measure the compressed height. If the spring is too tall it must be replaced. If it is not over 1/2" too short it usually can be stretched. Springs can be brought back exactly to spec and matched with each other. A squirt from a can of spray paint will serve for future identification.

or

web page

Hope that helps