Hi folks,i'm new to this forum,i have a 1973 sherpa 250,i also have a BSA B25 in bits,what i need to know is can i swap the bultaco engine for a B25 engine.I rebuilt the sherpa engine twice first time fitted a Sammy Miller crank rebuild kit,this lasted 773 miles,then got my brother to machine an exact replica heat treated properly. Low down engine speed is fine but on the road the engine seems to 4 stroke i have the original exhaust pipe (fisrt long & second triangluar)fitted,or is there a way to make the sherpa run smoothly???. Any help will be appreciated. Yours ARTY