Semper, the pipe size is normally quoted in O/D, I/D of the pipe can vary depending on the wall thickness used. Cheap pipes have a 1mm wall, better pipes have a 1.5mm wall.

2 stroke jetting: pre 69’ all Concentric carbs were jetted with what later became known as 2 stroke jets. Needle jets and needles were different, also the spray tube (full slant for 2 strokes, flat for 4 strokes and half flat half slant on triple cylinder engines) . Apart from the addition of air bleed holes in the 4 stroke needle jet the jet wall is thicker all the way to the top of the jet on the 2 strokes. On the 4 stroke it thins out half way. 4 stroke jetting by its design burns a little leaner, but AMAL didn’t have this solution until 69. For this reason I always try and find out for what application people are using a carb for when I sell one, if they ask for a carb for a 67 or 68, I find out if any other changes were issued then recommend a carb from there.



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