Misc: Carburettors Phenolic Carburettor Heat Isolators Needed on a Twin Vincent

[craig]

A classic carb mount on a 50-70s era British bike parallel twin is the use of phenolic spacers on Amal carbs.

There does not appear to be a period use of these phenolic spacers on Vincent twins, in fact the mount studs are too short to allow adding them at the manifold surface.

My question is the 1970-2023 use of such spacers by experts over the past 40 years on Vincents an improvement of performance on the road?
If you don't isolate the mount bolts as well, is the spacer effective?
Should a 1/8 be used, 5/16?, 1/4"?

An item for use in hot climates?
An improvement when used with ethanol fuel?
Compression ratio dictate use of such?

 

[Alyson]

With the phenolic spacer you are in effect creating a thermal break between the carb and stub. If the majority of heat comes from the stub and not the cylinder/head combo then you should have a cooler carb. I understand that cooler is better than hotter. Also a slightly longer venturi then with the spacer. I don't see this hurting at all. Also, I've seen heat shields incorporated on /2 and pre /2 BMWs.

 

[Speedtwin]

The fuel in the Vincent Amal carb is in a hurry it is on its way to create noise.
The fuel is not at rest long enough to require the protection of phenolic spacers.
Ridden in temperatures north of 38 degrees c and never missed a beat.
Maybe some of the riders in the very hot countries like Ireland could comment.

Al

 

[highbury731]

If you are using phenolic carb spacers for heat insulation, I agree that in theory, there should be a thermal break under the manifold mount nut. In practice, British manufacturers did not do this.
My 1955 Norton twin has phenolic spacers between head and inlet manifold, and between manifold and carburetor (Monobloc). It does not have heat insulation washers under the nuts.

For my Vincent I have bought suitable manifolds for Monoblocs (or Concentric) and phenolic spacers between head and manifold, but not for under the carb.
I propose using fibre washers under the nuts, and extended mounting studs with cooling fins. Do a thing, do it thoroughly. Or maybe not.

On those Vincent/Monobloc manifolds, the clearance for a spanner is limited. What I have done is get some reduced-heat bolts and nuts made so that assembly of the carburetor onto the manifold is much easier. I pointed out this clearance issue to Ian at VOC Spares and what I did. He agreed that I had a point, and said he would consider getting them made for sale. No idea if he did so.