My bike when cold will start up, then once warm and get to a traffic light, it dies on me. Usually it would take a couple minutes to cool down then I could start it up again, but most likely die again upon stopping/going again. I recently had valves serviced, and previous oil fouled plugs, and new plugs installed but I think are once again re-fouled. My mechanic rechecked all fuel lines and could only guess that the problem is the Fuel Cut Relay. I haven't tested the new one just yet. But what could cause the sputtering down, and the oil foul plugs.

 

Baybe a coil isn't firing properly and burning off the sparkplug? Maybe there's valve stem damage? Not to say yuor mechanic did it or anyhting, But if your valve lash was bad enough it can put a slight bend in the stem of the valve. Are the valves closing properly? Have you done a compression test?Is there a valve that is starting to tulip (gets pulled into the seat)? Just a couple of things to consider.

 

valves should be good, had 1 new installed due to bad keepers.

 

Might want to check your valve cover gasket.
If you had work done, they could have left the orginal on.

I had this happen to me (oil on the plugs) and when looking at the gasket, you could see the cracks in it.
Replaced the gasket and its been running fine every since.

Its pretty easy to replace, just a pain trying to get a socket in there to remove/tighten the valve cover bolts.

 

got a brand new gasket. Today I rode through the mountains, now I am considering dirty carbs, "one month of sitting" while at the mechanics as I noticed when passing someone at full throttle it paused/hesitated at 6k then went up. When I was at a light , it cut on me and I waited until it cooled down and then turned up the idle to 2k and it seemed to do better in the city.