Washer under valve springs to make them stiffer?

[GW's Motorized]

Check the length of the springs. Springs from a gx50 or similar engine might fit

 

[DieselTech]

If you want to shim the valve springs on a 142f huasheng, I would stick to a max thickness of .030" & no more on your spring shim thickness.

I personally think .020" thick spring shims would be sufficient.
You can use hardened arbor shaft shims for spring shims.

 

[michael whiteman]

79cc Performance Parts

Affordable Go Karts

affordablegokarts.com

These guys have e different spring sets with different pressure ratings.
Check out the physical dimensions..........maybe they'll fit.