Typical slow fps questions.

[Construct]

all settings lowest FC9 linux no compiz running
nVidia GeForce 6100 nForce 430s
but im still getting slow jerks during play mostly during battles when a weapon HITs a target not really when moving.... its strange it will be fine then all the sudden bam during a battle it just goes jerky it seems to be a fps issue but i cant be sure... any suggestions?