Atlas Idle

Just replaced the monoblocs on my 67 Atlas with concentrics. What idle speed should try to set these for?
Thanks in advance.

Somewhere about 800 to 1000 rpm - not sure this figure is ever quoted anywhere.
Then reduce it down as required. Folks in hilly areas usually like a slightly higher idle.?

Tell us how it goes.
New carbs can give it that new bike feeling...

Can you give the slide # and main jet numbers also the needle ring info?

Are you using 30mm Amals? I also want to try Concentrics on an Atlas

Bob Z. said:

Can you give the slide # and main jet numbers also the needle ring info?

Are you using 30mm Amals? I also want to try Concentrics on an Atlas

Click to expand...

They are 30mm with a 200 main, 2nd position on the clip/needle. They did need to have the flanges and the inside throttle adjusting crew blank ground down a bit since the fit is tight. Once installed, the bike fired up immediately- 1st kick- and idled smoothly. I am very much an amateur mechanic, so installation and synch the slides was easy, and i still have a little work to do to get the idle right, but a very straightforward improvement. Got them at Morries place n Ringwood, IL, from Ed who rebuilt the motor for me and has been an invaluable help to me as i reintroduce myself to this bike.

The P11, which is an Atlas motor in a Matchless chassis, used concentrics and a distributor. The original specs for the carbs were wrong, though. The specs originally called for 250 mains, 270 without air cleaner, 107 needle jet and #3 slide.

The set-up should be:

930 carbs
200 main jet
106 needle jet, middle notch
#3 slide

You have to file down the dummy side of the boss for the idle set screw on each carburetor for them to fit. Atlas carbs are set a little closer together than Commando carbs

BillT said:

The P11, which is an Atlas motor in a Matchless chassis, used concentrics and a distributor. The original specs for the carbs were wrong, though. The specs originally called for 250 mains, 270 without air cleaner, 107 needle jet and #3 slide.

The set-up should be:

930 carbs
200 main jet
106 needle jet, middle notch
#3 slide

You have to file down the dummy side of the boss for the idle set screw on each carburetor for them to fit. Atlas carbs are set a little closer together than Commando carbs

Click to expand...

Concentrics should be left hand and right hand. A flat on the inside mount carb flange should be filed to fit.
200 main jets are too low, they should be set up for you particular area in the globe, only a third gear plug chop will determine if it is right or wrong.
Re idle, if bike has been rebuilt and has Magneto ignition check that the mag fires 0 and 180 degrees with disc, with no leeway either side. If out, it can/must be corrected, or you will chew a piston up.
For best results on idle, use a Colourtune (used in the dark!!!) to set pilot jet mixture, then get both slides opening correctly and identically, and set carb slide screws to idle at 1000 RPM