jetting
 

I have a stock 2001 XT600E and I recently fitted a Remus Grand Prix exhaust can, which I bought used. I repacked the can. When running at 5k revs in top if I bck off the throttle the engine dies for a split second. This unsettles the bike (and rider) especially if going into a bend.
What changes to the carbs should I make to fix this and get optimum performance ? There are no dynamometer facilities in my area,I live in Northern Scotland.
Any help is appreciated.

Bear in mind I have never needed to get inside the carb of my XT, but I've done it on other bikes. The general advice would be that the new can is flowing more gas, and therefore the bike is running slightly lean. Going up a size or two on the main jet and/or raising the needle a notch would balance things up.

raise the needle one level like blackdogzulu said, if you decide to change injector for larger one then find some better flowing air filter, and you got yourself a stage one tuning

By 'injector' you mean main jet, yes? And bear in mind that if you remove restrictions to the inlet tract too, the jet needs to go up another size (or so - it's all trial and error really).

I had straight-through pipes on the Bonneville and took some restrictors out of the airbox. I had to go up to (from memory) 130s from the standard 118s. I'd estimate I got another 5-6 bhp from that. But try raising the needle first, as that costs nothing more than a couple of hours fiddling.