Venturi gauze

Information relating to the Matchless G9 or AJS Model 20 500cc twin
Simkat
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Venturi gauze

Post by Simkat »

Hi, just bought my G9 and was surprised that there is no filter on the carb. Does anybody use a venturi gauze like this?
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Andy51
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Re: Venturi gauze

Post by Andy51 »

I use one on my 18S but to be honest, it's mainly because I like the look. It will keep out stones (and prying fingers!), but has no effect on the dust that causes 99% of the wear. Andy
Simkat
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Re: Venturi gauze

Post by Simkat »

Cheers Andy, is it normal to have no filter? This is my first classic bike.
SPRIDDLER
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Re: Venturi gauze

Post by SPRIDDLER »

You don't give the year of your bike (it helps to put the year and the model in your Profile) but as an example, for the '56 models it was an optional extra. See pages 13 and 14 of the Spares List here:
http://archives.jampot.dk/book/Spares_l ... G9_G11.pdf

As Andy said, they look a bit cool but with a mesh that size it really isn't going to do much filtering.
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Simkat
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Re: Venturi gauze

Post by Simkat »

SPRIDDLER wrote: Tue Jun 08, 2021 11:10 pm You don't give the year of your bike (it helps to put the year and the model in your Profile) but as an example, for the '56 models it was an optional extra. See pages 13 and 14 of the Spares List here:
http://archives.jampot.dk/book/Spares_l ... G9_G11.pdf

As Andy said, they look a bit cool but with a mesh that size it really isn't going to do much filtering.
It's a 1957 model, cheers.
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Eamonn
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Re: Venturi gauze

Post by Eamonn »

I recall reading somewhere that the primary purpose of these gauze covers was to prevent fires in the event that the engine "spits" back into the carb. The gauze prevents any flames from going outside the carb area and thus reduces the possibility of a serious fire.

As has already been said, as a filter they are ineffective!
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GSAX1
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Re: Venturi gauze

Post by GSAX1 »

To be able to stop flames the gauze has to be much finer, like in the old miner lamps.

https://en.wikipedia.org/wiki/Davy_lamp

Image
Mick D
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Re: Venturi gauze

Post by Mick D »

Hi

In my opinion that type of intake is purely cosmetic, by all means fit one if it floats your boat but be aware that it will restrict the air flow and you may need to compensate by adjusting jet sizes or mixture setting.

Regards Mick
Groily
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Re: Venturi gauze

Post by Groily »

GSAX1 wrote: Wed Jun 09, 2021 7:11 am To be able to stop flames the gauze has to be much finer, like in the old miner lamps
Beat me to it gsax, was looking for a pic to demonstrate same thing when yours popped up! (Humphrey D got all the credit and life-long kudos for the Safety Lamp, but I seem to remember reading it wasn't without some argy-bargy with another inventor who'd allegedly beaten him to it.)

Coarse gauze keeps large objects, wildlife, flapping coat tails, stray nuts and bolts (!) etc out, but that's about it I reckon. Pretty to look at though and I have liked them when I've had them on things.
Simkat
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Re: Venturi gauze

Post by Simkat »

Mick D wrote: Wed Jun 09, 2021 7:40 am Hi

In my opinion that type of intake is purely cosmetic, by all means fit one if it floats your boat but be aware that it will restrict the air flow and you may need to compensate by adjusting jet sizes or mixture setting.

Regards Mick
Thanks, yeah I did wonder if it would restrict airflow enough to need re jetting.
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