Hi Folks, hope you are all well,
It has been a while since I have logged in and given any updates, but I wanted to quickly let other veteran Douglas owners know - I am just in the process of making a small batch of Amac main jet holders - for Douglas HYD Amac (and similar Amac types), as shown in the photographs . . . and due to the massive recent cost increase in the cost of brass, and setup costs. . . I wanted to check beforehand, if anyone is actually interested - if so, I may consider making a slightly larger batch than I am currently envisaging.
If you do want to reserve one of these - it is very important you email in the next couple of days - paul.norman@racingvincent.co.uk, and let me know you are interested - otherwise I will continue with the small batch I am planning, and you will be fighting with other customers on my online catalog for the few I do actually make!
Background:
I am not an expert on the early Amac carbs . .. as fitted to Douglas 2 3/4hp models, as well as 4hp - but know there were numerous variations over the period 1912-25, as well as other types fitted. However, I believe the type shown in the photos were known normally as the HYD type, and I know the jet holder and carb body shown in the picture were listed in the Douglas catalog as definitely being fitted to 1919-21 models as 1644D part number (please correct me if I am wrong - anyone with more knowledge).
However, the point being, this type of main jet holder also secured the Amac float chamber . . . but unlike later Amal carbs with seperate floatchambers, these early carbs seemed to rely on an almost knife-edge chamfer between the bottom of the floatchamber and the main jet holder.
As you can see in the photographs - I show two original jet holders - one in very good original condition (although part of the spare carb I currently have reserved for another build) and the one that is fitted to my current build . . . and that one is not in the best condition - and inevitably is p*ss**g fuel!!!
Having looked at it closely - I cannot believe this is not a common issue . .. and actually the floatchambers I have seen have a machined bottom face that lend themselves to being secured by a flat, lipped face main jet holder, and red fibre washer.
Therefore - for my own project batch I am going to make an 'improved' jet holder, with a large (0.875") bottom lip and red fibre washer, and mill the hex at the bottom of the jet holder, to the same dimensions as the original Hex.
You can see in the second photo - I have now written the CNC programs for the first and more complex operations . . . and am just doing setup . . . the jet holder showing has many small changes to make, and then the hex to be milled, before satin nickel plating . . . but hopeufully you can see what I mean.
I have paid special attention to ensure the height of the main jet will go into the exact position the original jet holder puts it in, providing the correct (high quality) red fibre washer is used . . . but I will be supplying these with the holder, ready to fit.
The price of brass has gone through the roof in the last 6 months (a 4 fold increase on a year ago seeming quite normal!) . . . so I definitely dont want to make more of these than there is demand for - so let me know quickly if you might want one . . . I have not calculated setup time and material etc yet . . . but on a small batch I am expecting circa @£30 each plated with washer (current CNC prog writing time and CNC setup time has already eaten any profit I will make on first batch!!).
Final pictures are my own Douglas 1919-20 (loosely termed a TT Rep!) . . . not getting much time recently - but now fettling ready for the first trip on the road!
Best wishes
Paul
www.RacingNorton.co.uk