2-into1 Mk2. Amal setting for 850 low compression

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Hi Gents,

Just asking on behalf of my buddy who is using the above setup, which came off his combat motor and is now using on an 850 engine. I would appreciate any setting changes necessary to make between the 750 and 850 or what has worked for you. I will pass it on to Pete.

Cheers,

Thomas
 
If you are asking about changing carb jetting to suit a 2 into 1 exhaust system in place of separate pipes - for best performance, it might be necessary to advance the cam timing and that changes everything. All you can do with the carburation is to work through it systematically - as with any other set-up. Over-rich on the main jets then adjust the needles downwards until you get the cough, then raise them one notch. If you cannot get the cough, your needle jets are too big.
 
Hi
I ran my 850 mk2a many years with an Amal mk2 34mm main jet 190 needle 2A1 needle jet 107 slide 3.5 pilot jet 25 drop the choke size from standard 50 to a 40 you never said what size the carb is. 32mm will strangle the 850. But saying that I didn't realise how restricted mine was until I put twin premier concentrics back on , good luck.
 
Not sure this is helpful for the MK2 Amal, but my 850 is running 1 Mk1 Concentric 32mm Amal. A local shop that has experience with Nortons made some changes in the jetting when I took bike in to have it timed with a timing light. They swapped in a 280 main jet inplace of the 260 default. 106 needle & new needle jet. This seems to run pretty well on my bike. Plugs not fouling and lots of top end pull! I'm also getting extremely good fuel mileage...45-48 mpg typically on highways....important b/c I have a 2 gal. HiRider tank.
 
If you get to the stage where the plugs are fouling, you either have an oil problem or you are miles away from best performance.
 
Toronto: what pipes and airfilter are you running?
My bike has stock pipes with the balancer cross header pipe and stick reverse cone silencers. These have the permanently mould in mutes so the end openings are quite small compared to other Commandos I've seen.
Air filter is fresh Emgo paper type.
 
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