Mike

I replaced the twin cone and fitted only the single exhaust to the others. There is a question of warranty for you. I don't have any factory warranty as I build my own and yes I know (before others jump in) JJ won't sell JJ1400 kits with few exceptions. I'd really suggest shipping yours back for repair since it is so far down on thrust. Changing the exhaust should be OK but opening it up invalidates any warranty. Dave is right your turbine should be marked No. 700+?

Paul