Carburetor sizing

acotrel said:
There was a mention on a forum some years ago, that a BSA single performed better with a step in the inlet tract. However better performance can be achieved by quite minor adjustments. Personally I would not have the step, but if the port is reshaped to remove it, there might be no easy way back to standard. A tapered manifold might be better.
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Yes. I once did back to back testing on a dyno with tapered inlet tracts some of which had small upsets in the tube. If anything it improved performance. Possibly because the disturbed airflow improved mixing???

Anyway steps of 2 mm certainly did not hurt.
 
I suggest that many road bikes might be tuned a long way from the optimum for performance. And in fact they probably should always be jetted a bit too rich.
 

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