It was the only pic that I had to show the chromed slide.
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I won't comment too much on changing carburetors. Few are more adaptable than Mikuni. In respect to Amal I'd avoid entirely reaming metallic type material that soft. Boring with a perfectly honed tiny radius HSS bit is far more dependable size control. In the venturi or lower with fuel in suspension a slightly unsmooth bore isn't a guaranteed detriment, but a true cylinder is important for a slide.
Ol Joe Lucas has a reputation here too. We've known his Prince of Darkness nom de plume awhile; now he's also the Duke of Fuel Fires?