G9 carb

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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G9 carb

Postby mikeydpippin » Fri May 08, 2020 5:55 pm

Interested to see peoples thoughts on carb replacement or renovation.
I have a 1953 G9 the carb is an Amal 76ag 1a not used for many a year.
Do I replace all gaskets slides etc with the kit
Or get a replacement carb, if so which carb would be the best replacement.
Many Thanks
Mike
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Re: G9 carb

Postby SPRIDDLER » Fri May 08, 2020 6:11 pm

Well, as I've dropped in here after cutting my grass...….
Depends how worn the carb is.
I'd get a relatively inexpensive service kit and new needle and main jet and try it before splashing out on a replacement. After all there's no rush during the lockdown.
If I was replacing I'd go for a Monobloc, partly for the aesthetics. Concentrics always look to me like carbs for Jap bikes, my old Villiers engines or lawn mowers.

P.S. I'm out of my comfort zone with twins but the singles changed to Monobloc in '55 so I'd look up the Owners Manual for a '55 G9 for settings unless someone who know what they're talking about comes along.
I poke badgers with spoons.....from 2 metres.

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Re: G9 carb

Postby Groily » Sat May 09, 2020 6:43 am

The 76 is a lot easier to fit on the manifold with the forward sloping downtube under the seat, but a Monobloc is, I reckon, a better carb for not having the perpetual risk of drip drip drip from the banjo joint under the float chamber, and for having a better range of adjustment.
On my '54, with sloping tube, I use a 376 Monobloc, with jets and settings as per '55 like Spriddler suggests, and it's fine. The fiddly bit is getting the thing on and off. Some people find you have to use bolts, not studs (or one bolt anyway), to get the wiggle room required. Air filter fitment is another thing altogether though . . . not easy at all. I don't have.
In terms of costs, the Monobloc option is usually cheaper than a refurb of the Type 76 (Surrey Cycles are good though, should you want to retain it), although always more expensive than a concentric. But I don't think (from faint memory of trying it one time) that a 626 will go on.

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Re: G9 carb

Postby Beefheart » Sat May 09, 2020 8:20 am

I have been thinking about putting a monobloc on my 53 G9 but dithering for the reasons mentioned by
Groily. However after fitting one to my G3 (see my post of Wednesday) I will go for it. So I will be watching with interest Mike.

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Re: G9 carb

Postby Groily » Sat May 09, 2020 9:16 am

Here's mine. Dirty old beast, and ignore any mods/bodges (eg bronze ring up top which I made to sort out long-ago stripped thread, slightly manky throttle cable outer and plain nasty tank mounting stud on that corner!).
As you can see, a tight fit. I have in fact managed with studs, and nuts that really are flush with the ends thereof - but without a thick heatproof washer (if there's meant to be one). Just flexoid paper. Has worked fine for years ,
376 on Mod 20.jpg
although at one point I did use its original Type 76 - until I got sick of the drip drip drip.
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Re: G9 carb

Postby mikeydpippin » Sat May 09, 2020 12:05 pm

Many Thanks Groily think I will go down the Monobloc 376 route, One drip on the bike will be enough 🤪😜
I have contacted Surrey cycles
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Re: G9 carb

Postby ajscomboman » Sat May 09, 2020 12:38 pm

mikeydpippin wrote:Many Thanks Groily think I will go down the Monobloc 376 route, One drip on the bike will be enough 🤪😜
I have contacted Surrey cycles


Club are cheaper than Surrey cycles for carbs.

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Re: G9 carb

Postby mikeydpippin » Sat May 09, 2020 12:41 pm

Thanks Rob 👍
Would that be 1” or 1 1/16 ?
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Re: G9 carb

Postby ajscomboman » Sat May 09, 2020 12:48 pm

53 would be 1" you'd probably be ok to have it jetted same as a 55 model to start of with.

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Re: G9 carb

Postby Groily » Sat May 09, 2020 1:46 pm

carb data M20.jpg


As here, is what I did, Neill's book. An inch, yup, as for Type 76.
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