Allchin injector

I am about to embark on the manufacture of the injector for the Allchin 11/2" scale traction engine. I have been away from the model for a couple of years but remember that there was some difficulty about the one shown on sheet 17 of the drawings and described in the book. There's a lot of work in making this item and I wonder if any builder who has completed this part of the model can perhaps give me some guidance in finding a design that works.

Regards

Bernard