Back in 2008 I installed TAS EOB boards, including Puff N Chuff boards, in two MTH TK locos.
Both locos are doing the same thing. They will puff in time with the chuff and it looks great. Then they sporadically smoke continuously for several seconds, then return to puffing.
During this time the chuffs operate as they should so I suspect a problem with the boards.
Do you agree?
Many Thanks
Ward