A couple of problems for unsuspecting norton owners.

baz said:

I've often wondered about rubber mounted carbs on a rubber mounted engine

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Most of our classic Japanese racers have it, no problem. Frames are not made of rubber as many say. But it took some experimenting to minimize the separate float chamber vibrations on the Manx. Tried different stiff fuel lines . And layout as the fuel line to the Gardner moves with throttle position.

The worst situation occurs if a carburettor touches the frame or a bolt - rubber mounted or not. Some people seem to believe a large four-stroke motorcycle is substantially different from a small two-stroke motorcycle. However all the same things still apply. The ignition system and carb jetting are critical, they all need 6 gears if performance is wanted, and if they are tuned to perform, they need to be ridden in the same way - feed the throttle on.
I am very careful to never disturb the pick-up for my Boyer ignition system. The carburettors are jetted to suit the ignition timing. If the ignition timing moves, it is not easy to correct the jetting. Moving the ignition timing one degree by accident can affect the size of the hole you need up the centre of the needle jet.

Mike40M said:

Our classic Japanese racers have it.

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With that set-up, the vibration is likely to be low frequency.

acotrel said:

With that set-up, the vibration is likely to be low frequency.

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Why low frequency? The Honda mostly runs at 9000-12000, which is not possible on a Commando.

Maybe it depends a bit on the inlet side of the carbs? I have a K&N hanging on the carbs there. If I switch to the ham can, would the added support at the inlet cut the amplitude of the shaking?