EDIT: Vuldub recently pointed out that I never finished posting the carb vent mod. I've redone the entire post and 86'd the old ones as I've revised the mod a couple of times since. I mocked it up on a spare carb for illustration purposes, but you don't need to remove your carb to do the mod. Takes about 10 minutes once you gather all the parts. The same method serves both the old and new style carbs.
The stock setup. In water crossings the end of the vent tube gets submerged and becomes blocked:
Here's what you'll need to fix it:
I used cheap vinyl tubing for the pics. The white "tees" are 3-way 3/16" vacuum fittings, available at any auto parts store. Two weedwacker fuel filters (don't fuss over these, they're pretty generic. They're only there to keep the crud out) and an optional lower vent shutoff made from a drip irrigation valve from the local hardware store.
Cut 2 short pieces of tubing and attach them to the carb. Insert the tees, then either re-attach your existing setup or make up a new one from fresh tubing. Attach your new upper hoses to the tees, making one slightly shorter than the other so they'll line up one behind the other. Insert these into the end of your frame's backbone, just above the carb. Make them long enough to get as high up in the tube as possible. Adjust all your tubing lengths as neccessary to make sure it clears the shock spring on the right side and that the lower vent exits the bottom of the bike as before, but don't re-attach it to the J-tube. The J-tube is just a big crap collector/fire hazard and limits your fording depth even further due to its location.
When you're done it should look something like this:
Without the shutoff valve your fording depth is now the depth of your carb, rather than your swingarm. For really deep water you can close the valve and your fording depth becomes the backbone tube.
Don't ever use the valve without re-opening it after a water crossing. If you dump the bike your lower vent could fill with fuel and cause a bike fire. For the same reason, don't even think of doing away with the lower vents and only running the upper.
Note: If you're not into doing the full vent mod and just want to decrease your risk of stalling on flooded city streets, remove your lower vent hose from the "J" tube. You'll find the J-tube attached to the frame behind the motor. Cut about 2 inches off the tube and let it just dangle behind the motor. That way the end of it will stay out of harm's way and sheltered by the wake of your motor in shallow crossings. I'd highly recomend doing this even on a stock bike.
