Motorcycle Repair: 03 xr50, honda xr50, secondary coil

Question
Hello Gary,
I have an 03 honda xr50 that will start and run but after only about 5-10 min of riding it stalls out and wont start for about 10 min usually and sometimes not for a while. I do have a BBR cdi or rev box if you will on it. Im not sure what it could be i have been riding for a few years and have rebuilt motors but this one really puzzles me. also it usually stalls out after coasting down a hill and i do live at 5000 ft in mtns. Do you have any ideas?     Thankyou

Answer
Riley, Without a little process of elimination diagnosis it could be a couple of things. Intermittant fails are the hardest to find.Try a new sparkplug then take it for a spin when it stalls out pull the plug and see if it has lost fire,if not the valves may be to tight and you lose compression untill it cools down.If it does lose fire this could be the ignition system,  the stator,pulse coil the cdi,the secondary coil, even the resistor cap on the sparkplug wire that connects to the spark plug. If I remember right the valves on these bikes run a close tolerance like .003 thousanths on each valve.There isnt much clearance so as the valves seat in the clearance goes away.