Mmmmmm, I have found a new feature on the XT.
I can only keep it at 70mph for about 1/2 a mile. It then seems that the carb resevoir runs dry.
So, I have to slow down again and let it fill.
Initial investigations have shown that the float level seems to be correct. The next step is to replace the fuel line, that has an in line filter, with one with no filter.
I was going to go an get one today, but it was pouring with rain and I could not be arsed.
As an aside I did get my Rukka trousers back from repair so could have tested them out to see if they no longer leak.