Hi. I have a NSR250 MC18. Sothing very weird started a few weeks ago. It was obvious the right side pipe had no fire and the power was non-existend. Took it to workshop, they replaced sparkplugs and cleaned the fuel line. Afterwards is was fine for a few days. Now the left side is dead / no firing.... I've check the plugs are there are spark. Can this again be insufficient fuel to the other side? Any ideas will be appreciated.

Many thanks