900 Series Concentric data for 650SS

Try a 220 and see how it goes. 250s are recommended for Monoblocs and the rule of thumb is 15% smaller for concentrics but for out wonderful alcoholic fuel it's probably better to go up a size, hence 220 for starters. Gordon.

ian, i cant remember settings but found out the hard way you probably will need twin 928 [28mm] concentrics. it took me months to find out the supposed magneto fault was the plugs fouling with 930 s fitted when i bought it. it would run fine on choke then die when engine got hot.i had a std pancake filter fitted for twin carbs.

In the Norton handbook the P106/P on page 85the settings for the 650ss with 930 Amal Concentric's are as follows. Main jet with air cleaner 260 with out air cleaner 280. The pilot jet is 25cc, throttle slide is a number 3, needle jet is 107 and needle position is in the central notch. The needle, needle jet, and needle jet holder can be up graded to the later Amal modified parts that give better pick up from lower revs. This consists of the following parts:-

622/124 Throttle needles two rings on the top. 622/122 needle jets with bleed hole. 622/128 Jet holder. Use the later type float bowls where the pilot holes got to the bottom, and half way down. The needle jet will also have to be smaller. All the above have to be used as they will not work on their own.

anthony the later 650ss might have had 930 concentrics but the early ones had twin 376 monoblocs which equate to 28mm. i also have p106/p but my handbook ends at page 75 with the atlas scrambler . so the head intakes must have changed sizes on the later downdraft heads. ian needs to measure his intakes before buying his concentrics. regards eddie

If you look in the F.W.Neil book this is printed with all the updated editions, with the concentric carb specs, as well as the later coil ignition systems. There was also issued as a supplement to the parts book that showed the new up dated carb and ignition data. This was later incorporated into the P106 handbooks to become the P106/P. I have fitted this carb size on a 650ss cyclinder head on my 600cc 99 motor and it runs great with these settings.

Agree with you for the carb settings for 930s, but really 928s are a more appropriate size and would need the smaller main jets.