[Mr Gazza]

Okay so the problem here is interference to the ECU from the coils, yes?

Do you perceive the interference to be a strong magnetic field or electromagnetic noise (RF or radio frequency noise).

If it is a magnetic field then I don't think a faraday cage will have any effect. In fact I'm not sure that it is possible to shield from magnetism?

If it is RF noise that is the problem, then there will be other sources of that from the bike in any case. So it is much more logical to shield the ECU (or whatever device is in question). Rather than the source of the noise.

A crisp packet will do this, but I daresay that you are after something a bit more sophisticated than that?
Aluminium foil will do the trick, provided that no inadvertent electrical connections are made with it.

A good way to do this is to first wrap the device with a rubbery type rigid foam, which will go some way to protect from vibration. Then wrap that with foil. Obviously leave the connection port(s) clear and preferably facing away from the coils... This also simplifies mounting the device, to a simple cradle or clip.
It is possible that some of the cables connected to the device might also pick up inference. Using coaxial cable will help with this. Or braided sheathing can be used. Again care must be taken to avoid an unwanted electrical connection, but the sheathing can sometimes be deliberately employed as an earth.

The mesh shield that you propose might not be effective against RF noise. There is a relationship between the RF frequency and the hole size in the mesh. and as the RF noise in question will be "White Noise" spanning a range of frequencies, it might well let through a fair bit of it. (or even all of it!)

Edit.... Carbon fibre will shield RF to some degree, but not totally.