I have been thinking ages for a decent fix for the tubular 'tower' part of the casting that the main jet fits into on the CB500 627B carbs and 400/4 carbs. You often get otherwise lovely condition carbs with the end of that alloy 'tube' moth eaten with corrosion, caused, I assume, by water in the fuel. (see attatched image showing what I mean) If I could find an aluminium filled epoxy that is resistant to modern fuels, that may be an option. I may try this stuff filled with ultra-fine aluminium powder.
https://uk.rs-online.com/web/p/potting-compounds/1991468/I also thought of a really thin washer of soft Viton that would seal between the top face of the main jet and the bottom face of the needle jet, that's assuming that there is a seal between the needle jet and the body. If not then how about an extra 'O' ring in the needle jet itself. The Viton washer would have to be really thin and the float height may need adjusting slightly to compensate for its thickness. A more radical option might be to solder the main jet to the needle jet but still fit the extra 'O' ring.
Building up with alloy low melting point solder is a 'no-no', as the carb alloy is lowish melting point too. I did think or slightly reaming out the alloy tower (or whatever it's called) and making main jets that are slightly oversize in diameter, withsuitably larger 'O' ring but there is not much 'meat' at all on that tower tube, even prior to it getting corroded.
Any more thoughts? I think Gerben in Holland just rejects any carb bodies with this kind of damage.
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This is the problem .. Otherwise decent condition inside the carb apart from corroded main jet mounting 'tower'
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