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I am working on a 78XS, the original owner (I am third) removed the air box an put on 4 individual filters. I have searched the forums and have anwered all my questions except 2. In the Clymers is shows tubing from intake manifolds on #2 and #3 cylinder going back to the air box connected to the ports used for carb synch, on the current set up these ports all have vent plugs, and of course there is no airbox on the other end. Q1 is what is the right plumbing here. Q2 relates to a copper fitting on the discharge of the #2 carb, it looks like this is connected to 3 other vac lines, 1 on each petcock and one coming out from behind the ignition cover area. Any guidance is appreciated.
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I have a bike and I am not afraid to use it -
VAC Lines
There should be a vac line from #1 carb boot to the left side petcock, a vac line from #4 carb boot to the right petcock and the one from the ign cover goes to the copper fitting at the #2 carb, this one is dampened for vac advance. The vac ports on #2 and #3 carb boots are capped. I use the individual filters and have good success. There are two fittings located at the junction of carbs 1 & 2 and 3 & 4. The bottom are fuel feeds the top are vents normally connected to the air box. In your set up, indi filters. i personally leave these open and pointed upward have had no problems. Hope this HelpsUnless you are the lead sled dog the view never changes. -
That was quick! thanks. One follow up, is there a problem with tying the petcock vacuum back to the dampened vacuum used for the advance? Splitting up the fuel valve vacuum back to intake manifold 1 and 4 is no big deal but the plumbing is pretty clean the way it was run. The guy also put a Y in on the two lines out of the carbs, the other branch goes to the fuel tank overflow at the back near the seat, and the main is run down by the swing arm, this looked good so I was goind to leave it.I have a bike and I am not afraid to use itComment
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The problem with running a petcock vacuum line from the dampened vacuum nipple on carb #2 is that the vacuum advance then has to run from an undampened nipple on one of the manifolds. This is _not_ good. There may be enough vacuum to run the petcock okay, but you are going to have problems with the advance. I would also be a little concerned with having any vacuum nipples connected to the tank overflow line. That line collects and drains away any water that falls on the tank and gets in beside the fuel filler. You really don't want that going into your motor either....
Ken TalbotComment
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follow-up
the simplest thing to do would be swap the vac lines. Ign vac to dampened port and current vac line at this port to undampened source, cap remaining if it ran well before it should run better now. take Ken's advice disconnect the fuel vent lines from the tank drain and leave open. this provides the venting needed for cv carbs to gravity flow.Unless you are the lead sled dog the view never changes.Comment
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