It might also be the needle problem that the BF have. Have your dealer put in the correct needles. I've owned 2 BF's and both ran like crap until they corrected the needles. If that doesn't work, do what I did, sell it. Those things were nothing but trouble for me.

 

its the needle... simple dealer paid fix...

 

the needle caused a lean condition and backfired through the carb. and i already had this done and i double checked to make sure that it was done correctly. what i have is a backfire out the exhaust.

 

Also could try turning air mixture screw in on rear cylinder 1/8-1/4 turn increments
Did you try 155/152, 152/152, 152/150 or CDI with 158/152?