Bonneville America Backfire

Hi
I own a 2008 Triumph Bonneville America, and have just fitted new long Tor exhausts.
I’ve had the bike remapped, and the bike performance was much improved, certainly on the return journey.
My first ride out, only about 10 miles saw very strange results. The first few miles were great. I parked up for ten minutes then returned to my bike. The ride through town was ok apart from the very loud backfire every time I throttled down. ‍♂️
it wasn’t as bad as this before the remap, but only does it after I stop the bike and start up again.
Anyone got any ideas.
Cheers
Bern

 

Sorry should have said, it’s a 2008 EFI.
Cheers