coil swap - made it worse

[FlipFlopGriff]

Swapped my coil, as I had a spare Bosch, to see if it would improve my running. It made it run much worse straight away so I swapped it back immediately. It is the correct Bosch number so why could this be. Tempted to buy another but would it just be the same. Its for the BV not the 500 if that makes any difference.
Bought it off Tim at ACT as a spare only at the time.
FFG

[Barreti]

pinch the coil off the 500 and see if that fixes the problem Paul

I'm sure I read somewhere if you shake a coil and it sloshes about then its knackered. Might be worth doing a bit of searching to see if I'm talking rubbish or if that really is the case most of the time.