Yesterday I took my XR500 out for a ride after putting it back together. I got the bike as a box of bits, but the motor was complete so I did not muck around with it, other than new oil, plug etc. At first it seemed to go fine no slipping, but as time progressed it seemed to slip under load in first. It does not feel like the clutch as the bike does not rev with no movement, it seems more like a miss or something jumping a cog, but it has a new chain and the front and rear cogs seem to be ok. All other gears seem to be fine and it will lift the front in second. I stopped riding and let the bike cool down for a couple of hours and then took it for another blast up the hill and the problem was still there. Any ideas of where I should start to look?