Answer:

The breather that comes with the kit may not be ideal for injected engines, the tank pressurises during use to a very high level. As it is only a one way valve it only let air in as you use up fuel. The other issues is when there's a slosh of fuel it lets out a waft of petrol which really is not very pleasant.

The solution to this is to use something like this:

Mocal - Fuel tank valve 1/4 push on unions.

A fuel tank valve that allows;
1) air to replace fuel used.
2) air to escape due to heat expansion.
3) a positive shut off to prevent fuel escape due to splashing or roll over.

This is achieved by a two ball system one, hollow plastic. Valve must be mounted vertically.

Merlin Motorsport Sell these

It's a little bit expensive, however its a safety item. So well worth investing in!