Disturbed Air Flow

That’s why the famous ‘Shemozzles’ have eccentric velocity stacks that align fully with the carb throat and by pass the area you describe.

I once had a race bike that didn’t run well on the shemozzles for whatever reason so a tried doing exactly what you describe having read it in Triumph Tuning by Stan Shenton.

He’s what he says about it:


Here’s a pic from his book:


But I really cannot say whether or not it makes any real difference. I would however say that you have to be very careful as the chance of getting swarf / particles in the carb circuit is high.

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Triumph Tuning by Stan Shenton

There was a claim made that a step in the inlet port of a Gold Star BSA which was caused by fitting a bigger carb, gave better performance. But cause and effect are often indeterminate. My belief is that because you can hear the inlet working, what happens in the port must be sonic. A step under those conditions usually causes an obstructive bump in the flow. I use two 34mm MK2 Amals with 30mm inlet ports, on my 850. The inlet ports are tapered from 2mm per side to zero over the first 15mm.

cliffa said:

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Triumph Tuning by Stan Shenton

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Indeed. Correction applied !