Hi everyone I have a 1968 triumph herold 13/60 . Runs fine on tic over with Rocker cover breather pipe removed from air filter housing, but as soon as it is re connected the engine slows and then stalls . If the breather pipe is connected on a relatively short run it develops a miss fire and eventually cuts out all together, every time sooting up the plugs could this be due to lack of valve clearance?(I have noticed that there is no tapping whatsoever that I can hear)
Thanks in advance for any advice