Basically could be almost anything... Compression loss due to damaged valves, dirty fuel, bad sparks, clutch, injection system.... etc...
More data required:
Is it missing or backfiring?
Does it rev properly when in neutral
Are there any warning lights on the dash
Is the engine temp normal
can you smell something burning?
How bad is the power loss? Is the engine revving without delivering power or is is spluttering and stalling?
Its giving a backfiring sound. bhu bhu bhu bhu sound.
Engine temp is normal.
No warning lights.
Cant rev properly.