The Enya SS 15 BB diesel has a different head and carb from the glow (Super Sport) SS 15 engine. Maris Dislers did a review of this engine back in 2006 or earlier. Google his name and you can find his engine review of this diesel by Enya. Text, charts and photos in the engine review. Also some tips on increasing performance. I would guess the Enya 15-IV is an earlier design? Jack