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Vacuum Question (not getting gas)

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    Vacuum Question (not getting gas)

    I am wondering what may be bad if a bike is not getting gas? I am going to look at a couple used gs 850's that the guy says has a clear gas line on them but don't seem to be getting fuel. Claims he rebuilt the petcock and still no luck. What creates the vaccum? If everything is hooked up right could it be a seal in the engine out? I want to pick these bikes up if the motors are good as the price ain't bad but I don't want to if the engines are junk. He was starting them with a battery charger so I am sure he had a dead or no battery in them. Also what kind of compression should a 80 and 81 gs 85l have? One bike has 26k and is in real nice physical condition with title, other bike is a 81 850l with 44k no title. $900 for both. I have a 82 with 12k I could use the 81 parts to fix up and the 80 don't need anything other then a battery and for it to get gas so he says. What do ya think?

    #2
    100 psi per cylinder is minimum service limit, 125-130 psi is ideal. do the test with the throttle held wide open and all 4 plugs out.

    the fuel gets vacuum from the number two carb. theres a hose that goes down to it.

    On "prime" fuel should run in no matter.if it doesnt the screen could likely be plugged up in the tank.

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      #3
      The vacumn that operates the petcock comes from the carby's, as soon as the motor turn's over vacumn is created, so he either did not rebuild the petcock properly or the hose is not connected/leaking.
      My motor is in good condition so I have compression of 160-170, 130 would be still useable, anything closer to 100 has problem's.
      There could be charging issues,have a look through the "stator paper's"on this site.
      Good luck!

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        #4
        Thanks for the replies! I am going to go look at the bikes tomorrow and see what I am up against. I've hardly posted here but I much appreciate this site and your willingness to help people here!!

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          #5
          my mistake-manual lists compression on an 850 at 128-171psi, with a minimum of 100. the 1000 is 128-185 psi, so GSpauls bike is nearly perfect.

          most important is that they are similar between all the cylinders (ie-if 3 cylinders are 175 psi, and one is 125 psi, it may be hard to get a good idle.if all 4 are even all is good)

          when I bought my 850 it had 125-85-115-125 or something similar, so I tore it down and freshened the top end. now all is good, although Ive not taken the time to re-test.

          If the bikes are complete and in decent shape they'll be worth putting back together.

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