I recently replaced my fuel hose and installed a fuel catch can (from the tank overflow and carb breathers). Now, when I set the fuel petcock to ON, it leaks out of this part of the carb (see pic), it stops when I turn it to OFF.

That has nothing to do with the fitting of new hose... it's the float bowl drain. Check you remembered to do the screw(s) up properly on the other side of the float bowl.
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Andy.
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Either that, or your floats sticking and flooding, if your screws are tight, check theres no crap in the float needle.
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Hmmm ok, I didn't touch the float bowls, but I'll have a look. Thanks

Lesviffer750 wrote:
Either that, or your floats sticking and flooding, if your screws are tight, check theres no crap in the float needle.

No, that's not an overflow outlet, it's a drain outlet. Leaking from there means the screws aren't seated correctly. There's a small rubber O-ring that can fail too, but that will usually "weep", rather than leak.

If the floats are sticking then fuel will come out of the overflow pipes above the float chambers (on the left of the top casting).
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I thoroughly cleaned and reinstalled the carbs. Started the bike up, and leaked again. I noticed then the carb overflow hoses I had installed were kinking a bit. I removed them and the problem stopped. Would kinked hoses cause this, make sense?

OR perhaps it was the pinched line from the fuel tank overflow. Would this be plausible?

Hi
My 18 has been doing the same it was just floats sticking,they get stuck in the down position and then fuel level rises too high,
There is a small brass tube inside each float bowl that will flood excess fuel out if it,and through the brass bits you have highlighted,
Hope this helps,

The best remedy is to always put your bike on a padock stand. Then the bike is level and the floats don't stick. Worked for me
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Yes I understand it could be the floats sticking, so I cleaned them out. But the problem started and stopped around the time I installed a (pinched) overflow hose to my fuel tank. I'm wondering if this also might cause the problem. Thanks