flat spot
 

This is my first time on here,i hope someone can help.I ride a 1989 2kf,it has been running fine until a couple of weeks ago when a misfire/flatspot appered at 3000rpm when accelerating from cruising or a standstill.The bike had similar symptoms about 3 years ago when i replaced the ht coil and this cured the problem.Have done same this time but no different.Have stripped carbs and cleaned,checked filter in tank and in float bowl.Cleaned air filter,fitted new plug and cap.Still have same problem.Did notice when i had carbs stripped there is wear in the barrel of secondary carb,bike has clocked up 35000 miles.Any help appreciated.