Use of carb intake insulators

Hi
What are the thoughts in regards to using carb intake insulators on these N15 CS 750's?
Per the parts diagrams at Andover Norton (AN), the insulators did not go into use until the 1970 750 which uses the intake manifolds.

Seems to me all NHT with carbs that had orings at the manifold (? around 56 and on ) used insulators at the "head end" of the manifold/block.
My norton parts book shown no difference for N15 or any other NHT. Different part# maybe yes...
I certainly pay more attention when researching to the original Norton factory parts lists than to ANIL.

Dave
Good input in regards to books vs ANIL diagrams.
I found it in the Spare parts list for 1955 Model 7 and Model 88 Delux.
Does not show in illustrated plate TA, but lists under Cylinder Head, Barrel, Studs and Bolts.
Part number D12/984 Fibre distance piece for manifold Qty 2
A D prefix would indicate starting in 1949. So first twin started this part.

Off topic but interesting, it also looks like they used a paper washer T/A1 part number D12/727 qty 1 between the carb and manifold. I wonder if the original carb then did not have an o-ring? I cannot find one listed it the carb parts listing.

The monoblocks on this N15 did have o-rings, so I will be installing the insulators.

Thanks

oring carbs have the oring, plain faced carbs get the thin paper gasket only. The insulator always goes on the head end. Never the carb.

The early heads/manifold insulators are shaped for those head ports with 1.5 or 1.625 C-C hole spacing

Norton46 said:

Hi
What are the thoughts in regards to using carb intake insulators on these N15 CS 750's?
Per the parts diagrams at Andover Norton (AN), the insulators did not go into use until the 1970 750 which uses the intake manifolds.

Click to expand...

I have a handful of parts books, AMC and Norton, going back to 1960, and they all show the part 23358 as a thin spacer. Once you get into the Commando parts manuals, this thin spacer is now called a Carburetor heat insulator, with part #NM23358. This doesn't change until Norton started using 32mm carbs, where the new part # is 06-2700 for the combat, 06-3458 for the 850.

You are correct, the Amal sidefloat carbs for the Model 7 did not have an o-ring.

We diverge a little though = history....

Norton46 said:

D prefix would indicate starting in 1949. So first twin started this part.

Off topic but interesting, it also looks like they used a paper washer T/A1 part number D12/727 qty 1 between the carb and manifold. I wonder if the original carb then did not have an o-ring? I cannot find one listed it the carb parts listing.

Click to expand...