Slide Wear Indications
Example: KTM 640LC4 Mikuni BST40
Left is new. Right is worn with under 20K miles (32,187 km) (claimed). The worn example has the slide lift holes drilled from 2.5 mm (0.0984")(4.91 mm²/0.0076 in² per hole) to 3.18 mm (0.125")(7.92 mm²/0.0123 in² per hole), increasing the slide lift area by ~61%, which dramatically decreases slide damping, thereby increasing flutter and as a result slide, slide guide, emulsion tube, and jet needle wear. The jet needle hole is worn by 0.16 mm (0.0065") from 3.37 mm (0.1325") to 3.53 mm (0.1390"), which is due to slide guide and slide wear causing the slide to be constrained by the needle in the emulsion tube. Notice severe grooving to the same worn slide in the engine side view below (contrasted with the subsequent image of a new one).