KTM 640 LC4 Mikuni BST40 slide

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.

new, engine side view

used, engine side view

late DR650 vs. LC4

slide guide, new

slide guide, used

emulsion tubes, new and used

jet needles, new and used

New BST40 slides can be purchased here.

Applications list:

KTM 400 LC4-E '01
KTM 400 LS-E/mil '04-'05
KTM 400SXC '00
KTM 625SXC '03 (USA only)
KTM 640 Duke II '00-'07
KTM 640LC4 '98-'99 & '02
KTM 640LC4 Adventure R '99-'07
KTM 640LC4-E '00-'01
KTM 640LC4-E/mil '98
KTM 640LC4 Enduro '03-'05
KTM 640LC4 Supermoto '01-'05
KTM 640LS-E/mil '00