Also make sure your header from the front is properly seated all the way INTO the header from the rear.
Loosen the bolt\screw on the rear a little, then get a helper to grab both downpipes and pull them upwards (helper will sort of need to lie over seat with one arm hanging down on each side of bike) while you tighten the bolt/screw.
Loosen the bolt\screw on the rear a little, then get a helper to grab both downpipes and pull them upwards (helper will sort of need to lie over seat with one arm hanging down on each side of bike) while you tighten the bolt/screw.