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Mercury Downdraught Carburettor

Submitted by chas_goupillot on Sat, 30/12/2017
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Nortons - General

A merry Christmas to all,

I am currently checking-out the 930 concentric carb on my Mercury.

The jetting seems to be as per the book - apart from the float level.

The top of the float, when the float needle tab is depressed, is currently level with the top face of the float bowl gasket.

The information I have to hand suggests that the level should be .080" (2mm) below the rim of the float bowl.

Should the level be set higher due to the downdraught angle of the carb? If so, what is the level to set it at? The current level seems to be too high, as the top of the float will be touching the bottom of the carb body at the cut-off point.

Best regards,

Chas

Submitted by john_holmes on Sat, 30/12/2017

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Downdraft makes no difference as the main jet is in the centre where the level is unchanged, rather than float height I go by fuel height.

Submitted by chas_goupillot on Sun, 31/12/2017

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Previously john_holmes wrote:

Downdraft makes no difference as the main jet is in the centre where the level is unchanged, rather than float height I go by fuel height.

Thanks for info John- what fuel height do you use?

regards,

Chas

Submitted by john_holmes on Tue, 02/01/2018

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From the Amal site

The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl. Thus when the needle valve is being held shut by the tangs of the float, the level of the fuel will be between 0.17" to 0.24" (4.33mm to 6.35mm) from the top of the bowl.

So you get hold of a spare float drain plug, drill and tap for a spigot and tube and then run the tube up the side of the carb in the centre aligned with the main jet. Or you buy one ready made from Andover Norton.

Submitted by chas_goupillot on Tue, 02/01/2018

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Previously john_holmes wrote:

From the Amal site

The correct fuel level for all Mark 1 Concentric carburetters is 0.21" plus or minus 0.040" below the top edge of the float bowl. Thus when the needle valve is being held shut by the tangs of the float, the level of the fuel will be between 0.17" to 0.24" (4.33mm to 6.35mm) from the top of the bowl.

So you get hold of a spare float drain plug, drill and tap for a spigot and tube and then run the tube up the side of the carb in the centre aligned with the main jet. Or you buy one ready made from Andover Norton.

Thanks John,

That's the info I needed,

Best regards,

Chas

 



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