second chimp in space
Join Date: Jun 2004
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The one by the seat is a drain. If this is anything like the '87 750 I had then if you look inside you'll see this tube going up through the tank up to the cap, where there is a hole for gas to go down if you happen to overfill. Usually there's a hose here that goes down to around the pegs somewhere along with a few other drains.
On the petcock, the big one is fuel (bottom on your pic i think), and the small one is vacuum (left on the pic). The vacuum connects to a nipple on the front top of one of the carbs (probably #2). If all your carbs have a nipple (like the 750 did) then take your pick. The vacuum from the engine opens the petcock (there's a diaphragm in there, could be broken or dirty if the petcock's leaking) and closes again when you kill the motor. You can buy rebuild kits for $25 or so, or if you're gonna use the separate fuel valve you don't really need this hose at all and just put the petcock on prime. I'd personally fix the petcock. And make sure that none of the nipples on the carbs are left open or else that cylinder will run lean.
The electrical is for the fuel gauge like you know, and I'm not sure on the port on that, but it's probably a drain/vent. Give it the same treatment as the other drain.
As for routing the hoses, make sure there are no kinks, that all curves are nice and round, and that they stay like that when the tank is down. Shorten hoses if necessary.
boldly going forward 'cause we can't find reverse