1967 650ss head combined with 2 amal 930 carbs

As long as you engine is tipped forward like a Commando then yes you can use them but I doubt it is tipped forward.

Checked on a -68 650SS engine I have. Funny, it has 30mm in head and 932 carbs. Nice finned and tapered manifolds. Probably changed by same guy who changed front brake to an italian 4LS wheel.

Mike

I got round the same problem by converting my 650 to a single carb. The special manifold has a 30mm end for the carb and narrows down to 28mm at the cylinder head end.

I get a lighter throttle, no mis-match of carbs due to stretching cables and more than 60+mpg on most journeys.

I know that this conversion is not correct with regards to the looks of a 650SS but it suits me and was well worth the investment. For the purists, my engine is from A 650 Manxman which had the option of twin or single carbs.

Stefan,

You would likely find that using 30 mm carbs with 28 inlet ducts will work okay. My understanding is that Norton intentionally specified certain Commando models with 30 mm heads and 32 mm Mk1 Concentrics, which apparently worked quite well. A larger carburettor than intake duct will work with correct jetting, whereas a smaller carburettor than intake could restrict performance.

Regards,

Andy

The 650 SS head was ported 1 1/8", but were supplied with 1 1/16" carburettors. They are reckoned to perform better with this carb size. Going 30mm Mk 1 Concentric is just too big.

Paul

30mm is on the big side. They will work but 28mm would be better. Like Philip, I too opted for a single carb manifold. A better option for the serious rider.

Previously paul_standeven wrote:

The 650 SS head was ported 1 1/8", but were supplied with 1 1/16" carburettors. They are reckoned to perform better with this carb size. Going 30mm Mk 1 Concentric is just too big.

Paul

The 650Ss head was ported to 1 1/8 inches but a springy steel sleeve was fitted to reduce the throat size to 1 1/16 inches. These were fitted with a pair of 376 monobloc carbs ( r/h chopped ). In 1967 when the 650SS got concentric Mk1's they were 930's. Before '67 I believe there was an option to have a pair of 1 1/8 inch 389 monblocs fitted without the sleeves like the Atlas had. Cheers, Howard

A pre-67 Norton 650ss or Atlas 750 with 1 1/8" Monoblocs would actually have a 689 (the /236) on the right. This is an exact mirror-image of the 389. It's a very rare carburettor

Paul

Previously howard_robinson wrote:

Previously paul_standeven wrote:

The 650 SS head was ported 1 1/8", but were supplied with 1 1/16" carburettors. They are reckoned to perform better with this carb size. Going 30mm Mk 1 Concentric is just too big.

Paul

The 650Ss head was ported to 1 1/8 inches but a springy steel sleeve was fitted to reduce the throat size to 1 1/16 inches. These were fitted with a pair of 376 monobloc carbs ( r/h chopped ). In 1967 when the 650SS got concentric Mk1's they were 930's. Before '67 I believe there was an option to have a pair of 1 1/8 inch 389 monblocs fitted without the sleeves like the Atlas had. Cheers, Howard

Hello Now the cylinder head on the 650 twins were made for inlet sleeves and carburettors of 1.16th 376/256and 376/257 chopped monobloc so the correct carburetters you needare Amalconcentric 928R and 928L, you get on more power with bigger carburetters get your jetting right concentric carbs have smallerjets to mono bloc Amal's yours anna j