Originally Posted by BergDonk
I had a similar issue with my BST40 that I chased unsuccessfully by leaning off the pilot. Fixed it with an FCR. Upon subsequent reflection, I decided it may have been a fuel enrichener aka choke problem. Maybe?
I was thinking about the enrichener as well, that's why I replaced the plunger.
Another thing I omitted to say is I'm using the IMS tank with the locking gas cap. Often when I take off the cap, I can hear the hissing sound and see the tank collapse a little bit, as the pressure is released. Maybe this pressure that builds up in the tank can affect the mixture as well?