Jawa 350 BS6 has lost its low-end torque and feels sluggish. Anyone faced this?

Hi everyone,

I'm facing a strange issue with my Jawa 350 BS6 (15,000 km) and I'm wondering if anyone has experienced something similar.

Over the last few months, the bike has gradually lost its low-end torque. It starts normally, idles smoothly, and there are no warning lights, but the engine no longer pulls like it used to.

In 1st gear, the bike starts feeling weak after around 15–20 km/h. In 2nd gear, it becomes hesitant around 25–30 km/h, and in 3rd gear around 40 km/h. It still gains speed eventually, but it feels like the engine is under a heavy load or something is holding it back. The acceleration is sluggish, especially when trying to pick up speed.

I'm now starting to notice the same lack of power in the higher gears as well.

I've already:

Replaced the spark plug (iridium).

Replaced the air filter.

None of these solved the problem. I've also noticed my mileage has dropped.

Has anyone faced a similar loss of low-end torque or sluggish acceleration on a Jawa 350 (or another fuel-injected bike)? What was the actual cause in your case—valve clearance, injector, fuel pump, TPS, ignition coil, sensors, or something else?

Any advice or shared experiences would be greatly appreciated. Thanks!