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    #1

    Need help desperately

    I just changed my head gasket on a 1981 gs850g, and put everything back together. The only confussion was with the gas tank. There are three hoses coming out of a gas tank: two on a petcock and one on, what I think is, fuel gauge. There is a thicker hose coming from the middle of the carburetors and I am assuming that it goes to the big conenction on the petcock. Where does the smaller one, coming from the carburetor (in between 1 and 2) goes to? To the petcock or the other connection?

    Also, what are two electric connections for? I ripped one of them and don't feel like fixing it unless I have to. I just want to get the bike running for right now.

    So I tried to crank the engine, but nothing. I think I have no fuel coming to the carburetors. When I open the bolt on the bottom of them, no gasoline is coming out.

    This whole thing is not very clear to me. How come no gasoline is coming out when tank was off the bike in the on position?
    What is "primer" for? I really need to get my bike running today, so any help is very appreciated.

    Toolman
    Tags: None
    #2
    The smaller hose is probably a vacuum line for the petcock. It should go to the carbs. The vacuum from the carbs opens a valve in the petcock to allow fuel to flow. Fuel will not flow in the "on" position unless there is vacuum on the smaller hose. You can check this by sucking on the small hose while in the "on" position. Be careful, if the petcock is bad you may be sucking fuel! Fuel should flow freely in the "prime" position..........no vacuum needed. The third hose is an overflow for the tank and should route behind the engine near the swingarm pivot. The wires are for the fuel gauge.

    Just a suggestion, when disassembling parts, make some drawings or snap some digital pics. It always seems like you'll remember how it came apart.............until you try to put it back together.

    Hope this helps,
    Joe
    IBA# 24077
    '15 BMW R1200GS Adventure
    '07 Triumph Tiger 1050 ABS
    '08 Yamaha WR250R
    "Krusty's inner circle is a completely unorganized group of grumpy individuals uninterested in niceties like factual information. Our main purpose, in an unorganized fashion, is to do little more than engage in anecdotal stories and idle chit-chat while providing little or no actual useful information. And, of course, ride a lot and have tons of fun.....in a Krusty manner."

    Comment

      #3
      A little more clarification
      there are two lines to the petcock, one larger than the other, the larger one comes from the petcock and goes to the fitting between the second and third carburetors.
      this is the fuel supply line.

      the second smaller line is the vacuum supply line to the petcock, it goes from a vacuum port on the second carburetor to the petcock control valve.
      it operates the petcock turning on the gas when the engine is running.

      with dry carburetor bowls you will need to turn the petcock to the PRIme position, the prime position is when the arm on the petcock is pointing to the rear of the bike, if your petcock has the ring in the arm you will see the letters PRI in the ring.
      put it in prime for about 10 seconds, then set it forward to main, or reserve depending on how much gas you have in the tank.
      If you don't prime the fuel bowls when they are run dry, or after carburetor work you will have to crank the engine for a extended period of time.

      the third line coming from the inside edge of the tank is the safety drain line for the fuel Gage, it is there in case the sending unit develops a leak, it will drain the leak behind the engine, instead of on top of the engine where it could start a fire.
      the two wires are for the sending unit for the gas Gage, the Gage wont work with out them both connected.

      Comment

        #4
        One more piece of clarification ... I don't know if your '81 petcock has a lever or not, but on my '80 there is no lever (although you can still see "pri" marked on the petcock, and it looks like you can use a screwdriver to turn the "valve" inside) and I have been told that on this type of petcock it doesn't matter what position the "valve" is in because the entire thing is automatically vacuum controlled.

        Oh, one more thing... don't assume that the petcock is bad if you suck on it and no fuel comes out the other tube ... it may require more vacuum than the average person is able to "pull" by sucking on the vacuum line. Best way to test it is to hook the vacuum line to the carbs and pull the fuel line off and drain it into a bowl while you crank the engine over ... you'll know almost immediately if it's working.

        Good Luck!
        Steve 8)

        Comment

          #5
          Thanks everybody for your great input. It turns out I had everything correctly. With your help I now actually understand how the fuel petcock works.

          It just took a little more cranking to get fuel to the carbs. However, I have a new problem: idleing too high. I posted the new message in this forum, so please take a look.

          Again, thank you so much!

          Comment

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