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Petcock vacuum line?

  • Thread starter Thread starter Anonymous
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A

Anonymous

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In a response to an earlier post I made someone mentioned the "petcock vacuum line" running to the #3 carb on my 79. There was no line running from the petcock to any of the carbs however there is a line attached to the number three as well as 2 and 4. The line(not the overflow coming from the float chamber, the line from the middle of the carbs) from 2 and 4 run down behind the airbox, is the line from three supposed to hook to the petcock?
 
How many hose connections on your petcock? If you have 2 then the smaller is a vacuum connection that goes to #3.
 
Also, there are two possible connection points, one directly on the back of the petcock, which has a hose connected to it, and one other which seems to come out of a "round place" under the tank. Which one is the vacuum connection?
 
kevin mannion said:
Also, there are two possible connection points, one directly on the back of the petcock, which has a hose connected to it, and one other which seems to come out of a "round place" under the tank. Which one is the vacuum connection?
Click to expand...

The one coming from "a round place under the the tank" is the tank vent.
 
When I connected the vac line to the petcock, upon turnover it sucked a huge amount of fuel out of the tank and deposited it on my garage floor, all without even starting!
 
Upon close examination I found that the hose that was connected to the petcock(not the vac hose) was purposely plugged. When the fuel is turned on gas free flows from the vaccuum connection nipple. Can this bike be ridden in this state? I rode about 125 miles on it in this current "set-up"(no vac connection, plugged hose in place) before I ran into problems, whether caused by this "set-up" or not I am not sure. Will rebuilding the petcock solve this?
 
That being the case You need to repair the petcock, recheck bike then recheck the floats- needle & seats if needed. Both petcock repair $25kits and aftermarket fuel valves $50 are available or the popular pingle replacement $100 Check with one of the many online part sources
 
Either the diaphram in the petcock has been removed or has a hole or tear in it. That diaphram is manipulated by vacuum pressure to serve as a valve to shut off fuel when there is no vacuum and allow fuel to flow under vacuum.

Someone probably took the diaphram out for whatever reason to allow fuel to flow though the petcock without vacuum being applied. As long as your float valves in the carbs are sealing tight you can likely get away without the petcock working properly. Just make sure the port on the motor side of the carb that supplies vacuum is plugged and the port on the petcock is plugged.
 
You Can ride it with the vacuum pluged. DO NOT leave it that way The needles are not designed to have the fuel left on while not running. You could end up with a tank of gas all over the floor or in the crankcase. Fix it and eliminate it as a problem
 
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