monobloc settings to suit Newman fast road cams.

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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monobloc settings to suit Newman fast road cams.

Postby Harold2110 » Tue Nov 17, 2020 2:07 am

Greetings all,

My 18s project is progressing well since I quit work for a semi retirement.
The engine is complete and now requires a carby.
The monobloc that came with it is worn and past its use by date.
I plan to replace this with a new monobloc from the store but would like some recommendations for jet sizes for to suit the Newman Fast road cams that are fitted.
Would anyone who has this combination be able to suggest a starting point for sizing.

Regards Harold
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Re: monobloc settings to suit Newman fast road cams.

Postby Andy51 » Tue Nov 17, 2020 2:00 pm

Hi Harold, I run SH (competition, scrambles) cams in my '54 18S and use standard settings for carb including jets as per that year's parts list. At a guess these cams are pretty similar to Newmans fast road cams so I suggest you try book settings. I have also fitted a Concentric Mk 1 carb and the settings were derived from the conversion formulae out there on the web, if I remember rightly it's Monobloc settings plus 20% but check. '55 models used Monobloc carbs and the parts list for that year will give you the settings. I believe settings only started getting wildly different with the introduction of the 86mm bore G80C in '56. Hope this helps, Andy

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Re: monobloc settings to suit Newman fast road cams.

Postby Andy51 » Tue Nov 17, 2020 4:21 pm

Hi again Harold, just been looking at my Amal Reference Catalogue and for '54, all 18S/G80S models (road, trials and scrambles) used same carb with same settings - 1 5/32 89N/1ED, 180 main jet, 106 needle jet, needle position 3, throttle valve 29/0624. In '55 CS models went for 10TT9 carb, but other models used Monobloc 389/7; main jet 250, needle 106, slide 3 1/2. I use 300/930 (30 mm) Concentric Mk 1, main 210, other settings as for Monobloc. Andy

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Re: monobloc settings to suit Newman fast road cams.

Postby Harold2110 » Wed Nov 18, 2020 1:02 am

Thanks Andy,

That looks like a good setup to start, I'll order a standard Monobloc.

Regards Harold

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