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Petcock flow issue?

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  • #1

    Petcock flow issue?

    Hey everyone, after having the kat apart for quite a while I'm getting everything put back together and came across an interesting issue that I hope I'm just being an idiot about. Replaced my fuel petcock and put 2 gallons of gas in the tank. When syncing my carbs, I noticed that I'm only getting fuel flow out of Prime and Reserve petcock positions, but not the ON. If memory serves, reserve hits when there's about 1 gal left in the tank. Is there any other reason, apart from simply needing to add more gas, why I wouldn't get fuel out of the ON position?


    Also, I noticed that when using the fuel provided to me in Reserve, it was too much and 1 carb overflowed. Float height is spot on 13 mm per the manual, new carb seals, A/F screws at 3 turns bc of DynoJet jet kit. At first I suspected it was because of the fuel filter I bought (a largely oversized Wix filter), so when testing with my previous filter it seemed to be okay, although I never went full reserve, maybe the 7-8 o'clock position on the valve. Any thoughts on why the carbs would flood on Reserve?


    Like I said, it's been a while since it's been running and I've been working on the bike so dusting off mental cobwebs of what to do.
    "Coffee should be black as hell, strong as death and as sweet as love."
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  • #2
    clogged petcock?
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    • #3
      The RPMs have to be over 800 for the vacuum system to pull gas in the ON position is what I read. Also even if you have no petcock and just a straight gas line the carbs shouldn't over flow. If they do overflow that means you are getting fuel in the oil. Check the float needle seat oring if you haven't replaced that one already. If you did make sure the seat is fully seated as far down as it will go.

      But yeah I don't have a petcock when syncing carbs, just a hose putting in fuel. No leaks here doing that. Something inside your carbs is causing it to overfill.

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      • #4
        Originally posted by 92xjunker View Post
        clogged petcock?

        I hope not, considering I bought it new. I'll keep this in mind though.

        Originally posted by Xerrith View Post
        The RPMs have to be over 800 for the vacuum system to pull gas in the ON position is what I read. Also even if you have no petcock and just a straight gas line the carbs shouldn't over flow. If they do overflow that means you are getting fuel in the oil. Check the float needle seat oring if you haven't replaced that one already. If you did make sure the seat is fully seated as far down as it will go.

        But yeah I don't have a petcock when syncing carbs, just a hose putting in fuel. No leaks here doing that. Something inside your carbs is causing it to overfill.
        Thanks for the tip, I'll double check the o-ring again just in case.
        "Coffee should be black as hell, strong as death and as sweet as love."

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        • #5
          Originally posted by kat_pilot750 View Post
          I hope not, considering I bought it new. I'll keep this in mind though.
          Could just need more fuel.
          "I'm sorry, I didn't mean to upset you when I called you stupid. I thought you already knew..."
          spammer police
          USAF veteran
          If your a veteran, join the KR veterans group

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          • #6
            Originally posted by 92xjunker View Post
            Could just need more fuel.
            Could be. I just wanted to sanity check if there was anything else wrong that people could think of. I'll keep you guys posted.
            "Coffee should be black as hell, strong as death and as sweet as love."

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            • #7
              I had the issue of one or more of mine overflowing. It was that oring for the float needle seat. Replaced it, and made sure they were fully seated. The issue went away afterwards.

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              • #8
                I've never seen the 800rpm minimal for the vacuum to petcock to flow thing... pretty sure that's a false, cause the starter isn't turning the engine over at 800rpm, but it does still flow some fuel.

                The avg amount of fuel in the tank for the "on" position is over 1.5 gallons. It's very possible your didn't get exactly 2 gallons, and it's just not enough fuel for the on position.

                Keep in mind that fuel flow is also gravity fed, so ... lower the overall fuel level, the less pressure on the fuel flow.

                As for the leak, as mentioned... it's a float needle issue, not a fuel level issue. The carbs need to be check, cleaned, paying special attention to the float needles.

                Krey
                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 http://katriders.com/vb/showthread.php?t=96736

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

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                • #9
                  Hi all,

                  sorry for the delayed response. After taking apart the carbs, and inspecting float needle seat, o-ring, valve needle, float height, and everything I got the leak to stop. And as for the petcock issue, it turned out it was as simple as adding more gas.

                  Now for the next issue! (sorry for the long, drawn out story telling) The bike idles fine, although i'm pretty sure i have a vacuum leak (slightly bouncy idle which becomes very bouncy with choke on). When i had the sync tool hooked up i saw the vacuum in #1 going up and down, noticed that the clamp between the airbox and carbs could be tighter. Tightened it down as far as it would go and although there's still a bouncy idle with choke on, it's not as bad. Now for the kicker, whenever I'm riding, whenever i go past about 1/3 throttle or about 4-4.5k rpm, the bike has a noticeable loss in power and the engine/exhaust sound changes (similar to how rolling your r's sounds), almost like it's not firing on all cylinders. Am I correctly assuming this is a misfire?

                  My specs: 2000 750, yoshi pipe, DynoJet Stage 1 (yeah, i know....previous owner put it on), 5* ignition advancer), stock airbox + filter. The bike did sit for about 1.5 years before i gave it the TLC to get it back going. While it was down, i did replace the valve chain tensioner and checked the valves. My main suspects: another vacuum leak somewhere else, main jet, needle jet, upper diaphragm. Because it's directly linked to throttle position and/or RPM, should I include the coil packs and spark plugs in my investigation?
                  "Coffee should be black as hell, strong as death and as sweet as love."

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                  • #10
                    Might be a bad gasket between the carb boot, and engine. Glad you got the fuel leak to stop.

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                    • #11
                      Just a possible cause, arcing from 1 or more wires. I'd suggest running the bike at night with tank off, and you can clearly see if any arcing is happening from wires or the plug boots in the plug wells.

                      Next would be the carbs again, checking specifically the main air jet and jet holder tube to verify no restrictions there.

                      Krey
                      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 http://katriders.com/vb/showthread.php?t=96736

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

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                      • #12
                        Originally posted by Kreylyn View Post
                        Just a possible cause, arcing from 1 or more wires. I'd suggest running the bike at night with tank off, and you can clearly see if any arcing is happening from wires or the plug boots in the plug wells.

                        Next would be the carbs again, checking specifically the main air jet and jet holder tube to verify no restrictions there.

                        Krey


                        I haven't taken apart the crabs again yet, but just for sanity sake since it's been a while since the bike ran (turns out it may have been more like 2-3 years that the bike was down... poor Kat) and the misfire improved (I can actually accelerate now over 1/3 throttle) but it's still there. I checked the plug wires and coils with my super duper accurate analog multi-meter and the resistance across the coil primaries went straight past 0 a bunch of times but once got it to stay at 1 ohm (Haynes manual calls for 2-4) and comparing resistance between wires 1 and 4 I got a reading of about 17K ohms (manual calls for 30-40) with the caps on. Unfortunately, I didn't test with the caps off due to impending rain and I was working outside (no garage). I was getting the same readings on coil 2 for #2 and 3. Looks like coils/wires are at least one part of the overall issue.
                        Last edited by kat_pilot750; 04-23-2017, 06:50 PM. Reason: correcting ohms from manual
                        "Coffee should be black as hell, strong as death and as sweet as love."

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