dragonfly carb

[chippy]

I am currently a bit confused about carbs, I have a 375/37 fitted to my Dragonfly since it was built as stated on the Amal web and has always been fine. Recently I have built a BSA Bantam which requires a 375/31 which is a 2 stroke carb, it appears that a 2 stroke carb has a diagonally cut off mixing tube in the venturi instead of a square top one as I understand the 4 stroke should be, my Dragonfly is diagonal Can any one throw some light on this please ?

[eddie]

Hi Eric,
           Yes, that's right - the mixing tube for 4 stroke engines is usually square cut, whereas it is often cut at an angle on 2 strokes. Evidently, it is something to do with getting a clean pickup from tickover. As far as I am aware, the tube doesn't come as a separate part - it is part of the choke block assembly.
  Regards,
                Eddie.

[chippy]

Hi Eddie, Thanks for that, yes that makes sense, and thinking about that perhaps it would also make sense that a 2 stroke carb would not cause any detrimental effect on a 4 stroke. It did make me wonder if my carb had been got at. Just a point of interest, it appears that the 375/37 is listed for the Francis Barnett and James 150cc on the Amal web.
Regards Eric.

[Hampshirebiker]

http://porklips.org/~mason/moto/amal_specs.html
According to my list it should be a 375/007 for your bike. I've copied & pasted a link above.

[chippy]

Thanks Hampshire biker ,I haven't seen that list before , Now I need two carbs one for the Dragonfly and another for the Bsa Bantam.
Regards Eric.