On your fuel lines at r/h/r of engine they go from the solid metal pipes to flexy ones, the unions on there have o-rings inside them on the push to seal side, take them apart and i reckon you shall find both of them solid and cracked, if they are that is where it shall be drawing in air. the only other place they seem to draw air is the elbow connection that is through the chassis near the fuel tank this can be a pain in the arse to get to as the loom gets in the way.