I have 03 Z400 and have installed a R4 pipe and pro flow adapter with a kn filter. I put the 160 main jet that come with the pipe in and had to take off air box lid I would like to run with the lid due to the conditions I ride in, any suggestions or maybe some pros and cons on riding with the air box lid off or on.

 

I have a 300ex and I do alot of water and dusty riding. I found the best thing to do is to drill six 1" hole in your lid and box and buy the universal air box breathers by UNI filter. They come six in a pack and will provide you with plenty of extra flow with out worrying about water or dust gumming up your filter.