Don't be too hard on the good folks at SU regarding their manufacturing. They were cobblers - shoe makers - who entered into making carbs for the war effort (old school SUs used leather diaphrams). As with any industry, they had to find a balance between quality and production numbers. And given that a pair of SUs lasts a whole lot longer than most of the components in, say Djet fuel injection, I think they've done pretty well.

Re: reaming and rebushing yourself. It's a good exercise and you'll learn something, but don't expect success. Think about this: once you enlarge the throttle body to accommodate the larger bushings, the inside of the carb throat will no longer be circular. It'll have two areas, adjacent to the throttle plate, that aren't round; and unless you can figure out a way to make this not be the case, you'll have a wicked vacuum leak.

This is exactly the reason that Shayne and I no longer use ZTherapy rebuilt carbs anymore. The last several pairs we've tried to tune cannot be tuned. False air galore, minimum idle at 1500 rpms. Problems just like those you've described over recent weeks.

I have the fancy reamer, I have a handful of bushings, I have a jig, I've done it successfully on several pairs of carbs. And I don't bother anymore: I send them to Rhys. There's a vast difference between my being able to do it pretty well after more than a dozen attempts and his being able to provide something that's perfect right out of the box. Intall. Start engine. Drive car. Dance the happy dance.

At some point, I think it makes sense to recognize that we're creating more work for ourselves than is necessary, and that no amount of effort nor good intention will replace the need for quality components.

Best,

Cameron
122SC,444
Rose City