Amal gaskets placement ?

This is one of those questions with lots of possible answers.

On the early twin carb 650 Dommies there were paper gaskets to sit each side of the individual spacer/manifolds. plus heat insulators to go on the head face and an 'O' ring, with a touch of grease on the carb face.

I guess the paper gaskets were to help overcome any surface irregualities. So you could have an 'O' ring could sitting against a paper gasket and at the head face a paper gasket and heat insulator together.

The single carb set-up appears to be different with no obvious arrangement for fitting heat insulators between the manifold and head.

I generally ensure all the respective faces are flat and then use a smear of high temperature silicone in place of any paper gaskets.

I wouldn't recommend using paper gaskets if there is a rubber 'O' Ring. As Phil says, the mating surfaces need to be flat - if they are not, you need to face them down. This is fundamental and universal to cars and bikes. As the carb is new it's flange face should be nice & flat and the 'O' ring new, but you can check it with a straight-edge (or a ruler!). The manifold face is fairly easily flattened off once off the bike. I use either 1200 grade wet & dry or coarse/fine grinding paste on plate glass. I have used the samemethod forover 40 years on my Jaguar XK engines (alloy flanges, tappet shims and oil pumps) and bikes. The biggest mistake with all alloy parts is to over-tighten the nuts. Carbs only need the 'O' ring compressed - not tightened to within an inch of its life! It doesn't need to seal against a very high pressure or vacuum. This type of seal is used on many, much larger carbs on cars. E.g. 2" SUs on Jags! I have never needed to use any form of gasket cement. A smear of grease isthe mostthey should need between the faces. Make a point of checking the flanges anytime you take the head off.

Cheers, Lionel

If you use nyloc nuts you can resist the temptation to overtighten the nuts on the carb flange, the carb should still be able to be rocked up and down a slight amount one tightened. The late Triumph idea of using an oversize O ring and nyloc nuts is good as it reduces heat transfer more as the carb never touches the manifold directly.