Twin Carb inlet manifold

The inlet manifolds for all the hybrid models, that would be the N15, G15 and all the P11 series used the thinner inlet manifolds. The reason being the lack of space with an air filter behind the the air filter. The carburettor spacers thin are part number 23358. If you look in the Master Parts Book, 1966-1967-1968 on page 9 this gives the part number and the bikes that that fitted at the top of the page. The 650ss, and the Atlas used the thicker spacer 23872.These same spacers were used for both types of Amal carburettors, on both of the featherbed, and hybrid twins. 

I don't think that is quite correct Anthony.  I had a 1968 650SS that had a pair of Amal Concentric carbs with an Air Filter and it had the narrow spacers from new.   I think that the narrow spacers came in on the Featherbed heavy twins when the Concentric carbs were adopted. They also stopped fitting the tin sleeves with the narrow spacers.  Cheers, howard  

....to fit the two LENGTHS of inlet tracts to the same bike. You would have to find another set of mounting bolts, and of course make sure the inside dia is the same. Such is the needs of 'back to back' testing.  Don't forget the insulation washers!   Let us know the results.....

The master parts book for 1966-67-68 show the inlet manifolds for the 650ss, and the Atlas to be the longer ones. As the featherbed bikes used two type of Amal carbs the the parts book, would have shown a different part number for the manifold for the different types of carbs which it does not. I have a 600 Dominator with Amal concentric carbs, and it uses the longer inlet manifolds. 

The Master Parts book is clearly incorrect in this matter which is not surprising to me when so many changes to the models were all happening at Plumstead around those times.  It is simply not possible to fit the concentric type of air filter around the pair of carburetors with the long induction manifolds so they used what was available from the Hybrids.  Cheers everyone, Howard