Loose fire after 10 minutes of riden - 2004 Yumbo Dakar 200

Not much information here but the first thing I would look at would be your ignition coil followed by your stator. It is more likely to be your stator (they can build up heat then cut out only to cut back in once temps have dropped ) but this is harder to check whereas the ignition coil is easy to get to and replace for not too much money. Never hurts to have a spare coil around.
Testing of the stator requires a mulitmeter and a bit more knowledge. Replacement of the stator is much more work than replacing the ignition coil.