Dual Amal Concentric 932 carbs on an Atlas

Will dual 932 Amal Concentrics work well on a stock Atlas motor (w/Commando pistons) or should I stick with 930 Concentrics?
I'm replacing the single Amal setup currently on this bike with dual carbs and I'm leaning towards the 932's since they've already been re-sleeved and rebuilt.
The 930's I have are original but are in very good condition but will need to be rebuilt.

What manifolds do you have for it ?

Convential wisdom is that smaller carbs/ports are better here.
All you can do is try them and see how they work on YOUR engine.
All the advice in the world can't really substitute for this.
And if they are rebuilt, ready to go, what have you got to lose....

The manifolds are basically aluminum spacers, smooth on the outside, with a vacuum port and spigot on each one.
Ther'ye probably 1.5 inches thick. I see them on ebay all the time.

Why not? Late Atlases came with 930s.

You may have to jet them down a little

The 932's I have were originally going to be installed on my 850 which came with a single Mikuni.
I had them sleeved by Lund and rebuilt them but never used them because I installed PWK flat slides.
So I've got these 932's all ready to go.

The 930's I have are old (no float bowl drain plugs) that I bought from Kenny Dreer on ebay. They're in really nice shape and have very little wear but I'd rather not spend the $125 to have them sleeved if the 932's will work. I suppose I can just rebuild them and install them as-is.

So I guess my question is: Can the 932's work well with proper jetting or will they be a problem?

My "guts" say you will not like the low end throttle response, and perhaps the mid range also. Jetting them down might actually make them perform worse. But, as others have said, if you have them, it costs nothing to give them a try. Please keep us posted on results.

Slick

Late Atlas came with 30 mm carbs as standard.
The Commando with 9:1 pistons was eventually fitted with 32 mm carbs with a curved manifold that was 32 mm at the carb end tapering down internally to 29-30mm at the port end
An ideal situation if you are insistent on using 32 mms is to taper turn your existing straight manifold from 32 to 29-30mm to accommodate the bigger carbs-whatever you do, DO NOT open the inlet ports in the inlet side of the cylinder head to 32mm, you WILL slow the gas speed right down-don’t ask me how I know.

My 68 Dunstall atlas came with 32mm carbs. Dunstall cam less than a combat. High compression. 32mm ports. ran fine for me. Though I would not port the head except for all out racing.
I don't think you will notice much difference unless you slam the throttle full open and bog the engine.
http://atlanticgreen.com/dunstall.htm

I converted my Atlas to a Dunstall, and as I have previously quoted on this website, the Dunstall cam that Paul D sold me was junk, the SS cam that I removed was better when I re installed it, the drilling out of the cyl. head ports to 32 mm was a mistake, although I did use it for racing, it would have been better if I had taper the manifolds as quoted, and left the ports alone. For one thing the acceleration would have been better.

mschmitz57 said:

The manifolds are basically aluminum spacers, smooth on the outside, with a vacuum port and spigot on each one.
Ther'ye probably 1.5 inches thick. I see them on ebay all the time.

Click to expand...

Yes the 1" long manifolds are for the longer monobloc and the 1-1/2" long manifolds are for concentrics. That way if you install the factory air cleaner it still fits within the frame OK.