How critical is the cut-out needle jet?

The stepped spray tube can be found in just about every round slide carb fitted to a two stroke. It richens up the top end. From what I've read the main jet was getting too big and the stepped spray tube allowed a reduction in size. On Mk2 Amals the stepped spray tube is listed for two strokes as is a smaller air correction jet.

Dave

Interesting details in that Norton Commando Ultimate Portfolio publication from the web link
"The Commando started life with 600cc, 650cc and then 750cc vertical twin engines....."
"... the new Commando made its debut in 1977 and became Britain's first superbike"

Someone should have proofed that page!

The Dynatek ignition which is available for Harleys uses a vacuum operated switch to change the ignition advance curve when vacuum is low at wide throttle openings. The problem I see with that approach is in how to get the switch to operate properly in a twin carb system. When using methanol fuel in two strokes, it is often necessary to recess the needle jet to still capture the tip of the needle, yet not meter off it. I've seen the cutaway spray tubes in two stroke carbs, however did not think much about it.

Deckard said:

Interesting details in that Norton Commando Ultimate Portfolio publication from the web link
"The Commando started life with 600cc, 650cc and then 750cc vertical twin engines....."
"... the new Commando made its debut in 1977 and became Britain's first superbike"

Someone should have proofed that page!

Click to expand...

Unfortunately, that same comment could probably be applied to much written about Nortons !
I used to keep a red pen handy, to apply to books in my possession.
Bit trickier to apply to stuff you read on the interweb.....

At least here we can comment - even if its not always entirely welcomed !!

P.S. Thanks LAB.
I do believe I even have that MotorCycle Sport - somewhere.

Amal do list a two stroke spray tube but it differs from the 622/074 which is notched

The Two stroke tube 622/075 is best described as slash cut

Frankie17 said:

Amal do list a two stroke spray tube but it differs from the 622/074 which is notched

The Two stroke tube 622/075 is best described as slash cut

Click to expand...

Correct. The square cutaway was 850 Norton only.