Rubber Mounted Amals

Anonymous

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Why are the AMALs rigidly mounted to the vibrating engine. It seems that this causes premature wear on all the components - particularly the slides.

When I rev my 850 on the centerstand the carb tickler dances around. I hate to think what else is moving internally.
Of course when I rev the bike on the centerstand the whole bike jumps backwards a couple of inches. It's called character!

Wouldn't rubber mounted cards be better?
 

Ron L

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Yes, Amal Mk II's and all modern carbs are rubber (spigot) mounted. The vibration is worsened by the isolastic mounting of the Commando engine.
 

Anonymous

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TT,

You have a good question; I don't know why the AMAL carburetors are rigidly mounted to the Commando engine. I assume you mean why is it not mounted to the intake track in the head via a rubber transition piece like so many other non British bikes.

Rubber mounting the carburetors seems like a good idea to me.

Regards,

Jason
 

Anonymous

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Car rubber mounting

I do not think it would be a good idea to rubber mount the Amals on a Norton as it would amplify the movement of the engine (even if it will filter the vibration). I remember a -82 FXR Harley on which I mounted a Mikuni (old type, not flat side) and it was handling only by the rubber: at idle the poor thing was jumping up and down! I guess in order to to this on a Commando a outside bracket would have to use to hold the carbs steady, while filtering the small vibrations that harms most the slide/bore.
Philippe
PS: has anyone thought of installing an old type HArley carb on a norton? They 36mm, not too big, not high as a Mikuni or a SU...
 

Ron L

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Single and dual Mikuni kits spigot mount the carb to the Commando with no ill effects. The oscillations are apparently not at the proper frequency to make them move "out of phase" with the engine.
 

MichaelB

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Interesting post.
I am not sure, but I think the Proddy racer runs em rubber mounted. I know Norvil sells 33mm smooth bores with rubber mounted manifolds. I have wondered why this is. When going for maximun performance, they go to rubber mounts.
I hadn't considered the vibration / oscillation movements, but had considered the heat transfer from the head. By rubber mounting, the carbs are insulated / isolated from the head, keeping the carbs cooler for better atomization. Maybe???
It seems the guys in the know run em rubber mounted. Does anyone have a good explanation??
 
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If you want to go the way of the rubber mount you may find the info in this old post interesting. RE;setting up Mark two’s on their Norton’s Just look it up under old posts. I hang my carbs from o-rings off the frame to releave the strain of the weight and dampen vibes. norbsa
 
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MichaelB,

I think you hit the nail on the head; all the go-fast guys rubber mount carbs. For instance, Paul Dunstall of Dunstall Norton fame rubber mounted the carburetors on his racers.

And yes, rubber does keep the carburetor cooler as well as dampen vibration.

Regards,

Jason
 
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