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Riding on Pri

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  • Riding on Pri

    Hi, I bought a 93 Kat gsx 750f at a very low price but I know it needs a little work. The guy who sold it to me told me that when he rides with the fuel gauge on the position On , the bike loses power for some odd reasons. Now, before selling me the bike, his mechanic changed all the fuel hoses and spark plugs thinking that would probably fix the problem, but apparently it didn't. The only way the problem doesn't occur is when the gauge on the position PRI. He told me he's been riding that way for 2 years and never had any problems like that. Since he wasn't asking much for the bike, I took a chance but I would want to know what is the impact of riding on the PRI all the time?, and what should I be looking for to fix this issue? Thanks.

  • #2
    is the vacuum hose running from the back of the petcock to the vacuum port on the side of carb 4? that vacuum hose triggers the petcock to open only when the motor is running.
    mine was disconnected when i got my bike and had similar problems


    • #3
      riding with the bike on prime could allow too much fuel into the engine, especially if the carburetor floats aren't up to snuff. Too much fuel could foul plugs, lead to poor engine performance and increase wear on internal engine components. It may be working seemingly ok now, but there are problems if the bike will not run with the switch in the ON position. A carburetor cleaning and tune wouldn't hurt. It probably wouldn't hurt to make sure the screen on the petcock (inside the tank) isn't gummed up with crud. Also, and perhaps first, make sure that the vacuum line that runs from the number #4 carb (right side) to the back of the petcock is in good repair; ensure that a good vacuum signal is present when the bike is running. The petcock needs that vacuum in order to allow fuel to flow when the engine is running.
      "The Lord will be awesome to them, for He will reduce to nothing all the gods of the earth; people shall worship Him, each one from his place, indeed all the shores of the nations." - Zeph. 2:11


      • #4
        Not too sure on that model, i have an '04, but i do know that PRI is a gravity feed not requiring the vacuum from the carbs. If the set up is the same, there should be a vac hose running from the carbs to the back of the fuel switch which allows the vacuum to feed the fuel when running. Some other more knowledgeable might have some more detailed advice, but it is a start.


        • #5
          Ok, I'll take a look at the vacuum hose and the petcock.I'll keep you guys update as soon as I get some results. I'll be working on it tomorrow. Thanks a lot.


          • #6

            being i am new to my katana i dont think this is a dumb question and it sort of relates to this issue only a little off

            what postions is 3:00 on pitcock
            what postions is 6:00 on pitcock
            and what postion is 9 :00 on pitcock please

            thanks in advance

            I need to get more posts so i can get on some of the other forums


            • #7

              here ya go.
              "The Lord will be awesome to them, for He will reduce to nothing all the gods of the earth; people shall worship Him, each one from his place, indeed all the shores of the nations." - Zeph. 2:11


              • #8
                3 is prime 6 is on and 9 is reserve


                • #9
                  RUNNINInG the bike on prime will have NO effect any differntly than.. running the bike. Fuel is on either way, or the bike won't run at all. Prime does not force gas into the motor, it just bypasses the need for vacuum.

                  The only concern is when the bike is OFF.

                  IF... left on prime, and

                  IF... your floats are set incorrectly/needles are not working right...

                  THEN... your going to have gas flowing out of the carbs, possibly into the air box and out onto the bike and floor, or worse.... into the crank case.

                  If you only use prime when the bike is running, and turn it to the "on" posistion when off... you have no worries as you are mechanicaly making the petcock work like normal.

                  If it's the petcock that is the issue, you can purchase a rebuild kit from The_CyberPoet for cheap (like $25ish) that should fix the issue. There is a full pictorial of the process on this website.

                  93 750 Kat

                  Modified Swingarm, 5.5 GSXR Rear with 180/55 and 520 Chain, 750 to 600 Tail conversion, more to come. Long Term Project build thread

                  "I've done this a thousand times before. What could possibly go wron.... Ooops!"