Amal Mk 1 Carb

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Hi, I am running a Norton Commando 850 mk2a 75 with a single Amal mk1 concentric carb 932 and an RGM single manifold, does anyone else use this set up with success and can tell me what main jet they are running. Also i have a 3 cutaway.

Any help appreciated.

Thanks.
 

Tornado

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My 850 had this setup when I acquired it. Was just the standard setup MK1 Amal for the 850, jetting as per a dual carb setup. Bike did tend to run lean from my experience, but there were other contributing factors to header bluing, like some air leaks and my inexperience with tuning the carb etc.

Overall bike ran quite well with the setup and I put first few thousand miles on it with the single. Be sure to use the extra thicker type insulator gaskets between the cylinder head and intake manifold. I even placed an additional insulator at carb to manifold. This was after I had the throttle slide jam full open just after stopping to fuel up. Cranked the grip open by chance before starting and found it did not return to closed. Turned out the carb had become too hot to touch at the float bowl in the few minutes since shutting down. Heat must have caused the slide to jam. It freed up after a few minutes on its own. The big lump of alu that is the 1to2 manifold does not allow much heat shedding (less surface area than two manifolds) and can pass much heat to the carb when no longer moving. Never had this issue again after fitting the thicker insulators.

Anyhow, I now run two carbs as the Norton gods intended. Much more effort to get them dialed in and working, but the performance does improve noticeably.
 
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marshg246

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Hi, I am running a Norton Commando 850 mk2a 75 with a single Amal mk1 concentric carb 932 and an RGM single manifold, does anyone else use this set up with success and can tell me what main jet they are running. Also i have a 3 cutaway.

Any help appreciated.

Thanks.
The main jet is not overly important unless you ride at 3/4 throttle to wide open. For wide open throttle. you'll need between 220 and 260 most likely but without knowing the air cleaner, exhaust, timing, type of gas, etc. it's hard to say.

You *MIGHT* want a 3.5 slide and/or a 107 needle jet but I would prove that before spending the money. You probably want the needle clip in the center position.

Look at it like your one carb is 4 carbs - throttle open: 0-1/8, 1/8-1/4, 1/4-3/4,3/4 to wide open. See this: https://amalcarb.co.uk/downloadfiles/amal/amal_tuning_guide.pdf
 
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