Alternative carb for 54 G80S

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Alternative carb for 54 G80S

Postby AndyO » Sun Nov 15, 2020 2:46 pm

Hi folks,
My newly acquired G80 is now running without smoke following a rebore (thanks Andy Mitchell near Hereford) but I’m still struggling with the original pre monobloc 89N/1ED. New slide, needle and float valve needle. Fuel still dripping everywhere. All new washers etc. Everything ultrasonic cleaned. I’m assuming the float valve seat is poor. Can I “lap” the new valve?
Alternatively, if I was to fit an Amal concentric which one is best and what jetting would you suggest?
Many thanks
Andy
Matchless newbie

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Re: Alternative carb for 54 G80S

Postby Pharisee » Sun Nov 15, 2020 3:17 pm

Fit a 389 Amal Monobloc, 1.5/32 bore, 260 Main jet, 106 Needle jet, 30 Pilot jet, 3.5 Slide. Needle on middle notch.

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Re: Alternative carb for 54 G80S

Postby 56G80S » Sun Nov 15, 2020 5:48 pm

I'd worn out a Concentric and consequently couldn't get a decent idle and had some starting problems.

I got a 389 from the Club; fitted, started and barely any adjustment required. 1956 G80S.

Great.

Johnny B

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Re: Alternative carb for 54 G80S

Postby Andy51 » Sun Nov 15, 2020 10:28 pm

I use a Concentric Mk 1 930 carb, can't remember settings but can go and look in the garage tomorrow if you are interested. Andy

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Re: Alternative carb for 54 G80S

Postby Triumph-Legend » Tue Nov 17, 2020 8:12 pm

Monoblock. Club spares or direct from Amal.

It's the correct carb for the year of the bike and the work fine if not too worn out. Might need a bigger main jet for modern fuels to get best performance.

Concentric. Hmm, why fit a carb that was not around at the year of the bikes production. Also I think these never look right on the early fifties bikes.
Oh crap, I'm sounding like a rivet counter. :rofl:

However, it's your bike so go with whatever suits you best. The current Mk2 Concentric carb has a nice modern look. No idea how it performs though.

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