2 mm laser cut 101 copper gaskets for Jawa 350 (Type 638/639/640/classic/retro). With the introduction of E10 fuel in the UK we have noticed an increase in pinking (pre-ignition/detonation) under severe load. Typically pulling hard into a head wind or up hill, but also while maintaining higher speeds for a while. The reason is unclear, as ethanol has pretty good anti knock properties, so in theory all should be OK. The energy in the fuel is slightly less by volume so this might be why. We have had these gaskets made in the UK to help with the issue. They are thicker than the standard gaskets and therefore lower the compression slightly. We have not calculated the new compression ratio. In use the bike feels exactly the same but maybe slightly smoother. On paper power will be down by a hp or 2, but if you are using the maximum horse power all of the time you may have the wrong bike to start with. They will require a tiny amount of smoothing on the cut edges and softening with heat just before fitting

£15.00 per pair.