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Installing New Carbs
#816969 07/21/20 8:23 pm
Joined: May 2014
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qbeanie Offline OP
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Im installing new AMAL carbs on my 67 a65. The old ones were warped and i want yo avoid this with the new ones. How tight should the nuts be? Is there a recommended torque value or is just snug enough to crush the orings?

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Re: Installing New Carbs
qbeanie #816985 07/21/20 9:51 pm
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You can use nyloc nuts to hold tight and spring washers to set the torque, fit the carb , spring washer and nyloc, tighten each side evenly until the spring washer is just crushed flat, thatll do , you want the minimum that will stay in place, carbs are made of stuff like cheese , treat them that way.If you can still wiggle the carb slightly thats good, if if its solid tight thats not good.


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56 Norbsa 68 Longstroke A65
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Re: Installing New Carbs
qbeanie #816996 07/21/20 10:55 pm
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I use flat washers and reduced head nuts but each to their own. I tighten the nuts and ensure that the slides move freely. When they don’t i back them off until they do. The effect is the same as Gavin posted.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
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68’ D14 trials (undergoing transformation)

Re: Installing New Carbs
qbeanie #817030 07/22/20 8:19 am
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I went the Enfield way & tossed the O ring decades ago
So it is a thick soft gasket under the carb and do it up till just solid
The gasket extruded into the O ring hole and there is no fulcrum point to warp the bodies if they get over tightened.


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Re: Installing New Carbs
BSA_WM20 #817069 07/22/20 5:44 pm
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Originally Posted by BSA_WM20
I went the Enfield way & tossed the O ring decades ago
So it is a thick soft gasket under the carb and do it up till just solid
The gasket extruded into the O ring hole and there is no fulcrum point to warp the bodies if they get over tightened.

I used to do this but after a while the gaskets dried up like a biscuit, sometimes but rarely caused an air leak


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: Installing New Carbs
Allan G #817120 07/23/20 4:25 am
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Originally Posted by Allan G
I use flat washers and reduced head nuts but each to their own. I tighten the nuts and ensure that the slides move freely. When they don’t i back them off until they do. The effect is the same as Gavin posted.
Considering the cheese metal used for these carbs, just tightening until the slide doesn't move freely is probably enough to warp the body.


Stepping on others doesn't make you stand tall.

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Re: Installing New Carbs
qbeanie #817134 07/23/20 8:59 am
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Nothing wrong with the metallurgy.
The exact same alloy is still used for carburettors
It was a design problem with insufficient bracing between the flange & the body or the body being just that tiny bit too thin.
Then there is pig ignorance .
BSA originally fitted a light spring washer with a 1/2 nut to avoid over tightening
They got lost and were replaced with full nuts done up till the spannar broke cause you don't want them to leak or fall off.


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Re: Installing New Carbs
qbeanie #817175 07/23/20 4:30 pm
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Is the referred spring washer a split or belleville type?

Re: Installing New Carbs
qbeanie #817177 07/23/20 5:01 pm
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I have always done snug

If you have locknuts in place, you shouldn't have a problem

If in doubt, a little blue loctite does not hurt


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