Concentrics

R stands for Right, L for Left but looks to be missing from yours. Your left one stamped 10 is off a Triumph T120R 1969.

Our Atlas came as standard with twin concentrics and I could not get rid fast enough !!.  A cheap fast wearing bit of junk . A conversion to a single monoblock  was done ASAP  and not regreted. Sorry if thats a bit of a downer.

My 64 engined 650SS runs with a single R/H 930 and goes very well. 

Sounds like all that is needed is a 2-1 manifold and set up as per Mercury.

This includes a 280 main jet. You can also expect 70 mpg.

PS:  The new Amal's appear to be made so much better.

Is this what 'build back better' means?

If the bodies are good and it's going well, I would still change to chromed or hard anodised slides to reduce future wear.  I just swapped concentrics on my 88SS for monoblocs. It's a fiddly job. Cable outers are a different length. Number 1 is the top groove.

Monoblocs are more expensive but correct. If you have the bits to fit one type it's easier to stick with it because the cables are different.  Also it's cheaper to set up one and get that right first because the settings for two should be the same. My two concentrics on the 88SS show no obvious wear after about 10k miles with chrome slides. I've now fitted monoblocs for the sake mostly of appearance, but Phil ( of this parish) warns me that there is some evidence that the chopped float monobloc might lead to some fueling issues..more to worry about. The opposite hand monobloc is no longer made by Burlen.

Hi,

I have a pair of monobollocks with the chopped float on my 650, and there are times when making 'good progress' that I get some fuel starvation. What I don't know is whether it is the fuel tap, float valve or float chamber exit where the restriction lies. As it only occurs at sustained speeds above 5000rpm and full throttle, and the fueling is so good everywhere else, it isn't something I feel needs fixing in any hurry.

Biggest issue (if you can call it that) is that the mixture screws are hard to access on the left carb with a pair fitted. 

Regards, George 

I wonder if this is why the bottom intercontonnecting banjos take a bigger diameter hose than the main feed?  Is that a relatively modern update in an effort to solve the matter? I bought some nice new supply hose with mine, but couldn't finish the fitting.

No issues with my single Amal 930, set up as per Norton Mercury.

... one of those float extensions lying about if you want it for the price of postage. Might help with the fuel starvation issue?

Thanks Ian, 

I won't take you up as I use the performance drop off to remind myself I'm not 18 any more and no longer invincible (I like my licence and I don't bounce like I used to!)

Thanks anyway.

George 

Ian;  the RH is chopped as it wouldn't fit alongside the LH one which is whole,  and extending that  would not cure the issue.

David; try fitting a knurled TT pilot adjust to the screw.  All I did was bore the original screw enough to locate the cut down jet and put a cross pin in the shank to fit into the screwdriver slot. Once setup you can remove it. 

George:  I thought I had similar issues when on the gas,  suspected fuel flow (as per David above) wasn't sure so  removed tap which  was a  bit cruddy.  Fitted a clear fuel filter in line to see if I was creating debris in the tank and hey  presto  it  was clean art all openings. 

Either the tap cleaning or the fact that I had introduced a large plenum in the line by way of the fuel filter giving a slight increase in available fuel eradicated the problem.

Then there is always that miniscule breather hole in the filler cap???? 

Jon