theres a breather pipe that runs from the metering unit, all the way to the left side of the head, via the back of the inlet. its hard plastic and gets brittle. also theres one that goes into the back of the inlet thats hard plastic. Check these. you'll need a mate inside keeping it running, and you go round the engine bay with some carb cleaner / brake cleaner / wd40 and spray everywhere one part at a time. if the note changes you have an idea where to check. just remember its flammable with MFI its always 99% an air leak, the problem is finding it.