When the screw caps on the underside of the carburetor keep leaking (after having installed new gasket rings), then the probable cause is the condition of the seat of the carburetor gasket.

If you look closely, you will probably notice that the surface is rough, damaged or scratched.

The solution is NOT to further tighten the screw cap: the gasket ring is not flexible enough to fill these small damages.

The seats of the gasket rings can be machined, but if the damages are not too deep they can be removed by sanding the seat with a very fine grit of (water proof) sand paper. Use a sanding block to make sure that the gasket seat remains flat.

On some carburetors the screw cap of the main jet lies a bit deeper than the adjacent screw cap: when using sanding block, more material will have to be removed from this gasket seat to reach to the surface of the main jet gasket seat.

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