My bike died on me the other day. It had been running fine prior but on the day it died the acceleration was acting funny, slowing down intermittently. I was able to get it running by swapping out all of the spark-plugs and jumping the battery. Some of the old plugs were fouled:
From there I was able to ride it about a mile home without any problems. Left it sitting for a few hours and hopped back on, instantly the same problem again, jumpy acceleration, followed by the bike shutting down entirely. Parked it and checked all the spark plugs. No fouling, although some of them had the very slightest trace of yellow/orange residue.
Not sure why swapping the spark plugs completely fixed the problem for a few minutes. Not sure what to check next. Air filter is new, gas tank and carbs were recently cleaned, fuel lines are new.