If you can get someone to braze it, good luck. That is a brass line that is part of the choke circuit. It does need to be connected properly, or it will cause a huge vacuum leak. I had one broken, and one missing{!!!} on the B4 I bought for my daughter. I ended up getting another set of carbs. I'd send you a good carb, but I'm going to keep all of my parts, just as a down the road precaution. With those lines broken, it was impossible to get the bike to start using the choke. I had to turn off the choke and cheat with some starting fluid. The only carb kit I've found, was a "Keester" kit that had just the float bowl gaskets, and the fuel valve needles. A word of caution on those needles.
If you get that kit and use the needles, you may need to use them without the retaining clips attached. Either they were the wrong needles in the kit, or they were machined incorrectly {still wrong, eh}, the clips wouldn't let the needles seat completely, and you end up with carbs that pee all over the floor, and flood out the bike, literally, in short order. Do a bunch of snooping around here. There is a lot of info on these carbs here. They are known to be a bit fussy. There are 5, count em, 5 o-rings per carb, that as a good precaution, should be checked and replaced. You will find the o-ring info here. I found it cheaper to get the o-rings from a vender on line that happened to be down the street from me. The links below should help you along.
http://forums.banditalley.net/index.php?topic=10252.0http://forums.banditalley.net/index.php?topic=235.0http://forums.banditalley.net/index.php?topic=208.0
Topic: Carb Questions (Read 2461 times)