Home Forums Shifter Karts TM tuning issue

This topic contains 18 replies, has 6 voices, and was last updated by  John Kwong 2 years, 4 months ago.

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  • #80754

    Brad Clem

    I recently acquired a kart with a K9B after running a CR125 for a couple of years.  I keep getting the same running problem no matter jetting changes, float adjustment, plug gaps (just for testing), fuel pumps, lines, etc.

    So the problem comes up when I exit a long sweeping turn after a WOT section.  I hold the throttle about 50% through the turn, then return to WOT and it spits and sputters until I get slow enough, then it dies.  When I look at the fuel feed line to the carb, it is empty.

    The kart came with 2 Dellorto carbs.  Both act the same, so I put the Keihin from the Honda on it.  Same problem, but seems to need a sharper turn to develop.

    Yes, the gas tank is full.

    Any help would be appreciated.



  • #80756

    Glenn L Riggs

    Check pick up tube in tank and tank vent.

    • #80759

      Brad Clem

      Confirmed pickup tube is clear, no cracks in the line.  Vent is open.

  • #80769

    Matt Martin

    Has to be a fuel pick-up issue if it’s happening with three carbs.


    Fuel pick up system:

    – Pulse fitting (could be affected by reeds, or crank-case sealing)

    – fuel pump

    – feed/pick-up line

    – Pump-to-carb/return line.

    Have you restricted the fuel-pump return hose with a zip tie or clamp?


    can you post a photo of the fuel line circuit?

    Does the problem occur on left and right sweepers?

  • #80776


    Makes a lot of sense, I agree with the guys.

    I have a strong feeling it’s your pick up hose in the tank, even though it may look good, you may have a crack right at the top above fuel level, near the fitting, and when you turn on sweeper the “G” force the bottom pick up sideways and it opens up the crack up on top, causing the system to only suck air.

    Remove complete pick up set up out of the tank, remove bottom piece or block it, the slightly blow some compressed air through the top fitting, spray some soap or just feel for air leakage. I hope this does it for you. Good luck.

  • #80788

    Brad Clem

    – Pump-to-carb/return line.

    Pulse line and feed line (pump to carb) are new.

    Pulse fitting appears to be ok.

    2 sets of reeds and cages have been in it.

    Fuel pump is new.

    No static restriction.  No apparent dynamic restriction.

    Left or right, it does not discriminate.

    Output fuel line had a Y that fed carb and return, while blocking the other port at the pump.  I put a new pump on and re-routed pickup in, return out, carb out.

    The pickup tube was hardened and would not come off either end.  I just now put the one from the Honda on it (replace with known good) and will test at an autocross on Sunday.
    Thanks for all the replys.


  • #80793

    Matt Martin

    This is how I have mine routed, and have not run into this issue (I also have a slight restriction in the return line):


    TM K9 Fuel routing

  • #80803

    Brad Clem

    IMG_0638That’s a coupler at the bottom of the picture

  • #80806

    Matt Martin

    In addition to making sure there are no cracks in the tank’s pick up line (and/or bulkhead), I would suggest using a Y or a T to connect the both pump outlets to a single hose, then another Y to branch them back out.  One returning to the tank – with a restriction – and one feeding the carb.

    The only other thing I can recommended is if you have any in-line filters, to make sure they are tight, and not able to introduce air into the system under any kind of loading.




    • #80807

      Brad Clem

      I see that you are maximizing volume on the carb side of the pump.  I will reroute as you suggest.  I have a filter on the feed line to the pump.  Would this cause a loss of pressure?  Should I move it to the return line to increase fuel pressure fed to the carb?  Then change the carb screen more often.

  • #80813

    Matt Martin

    I would suggest the filter be on the feed line from the tank to the pump.

    My only suggestion there is to inspect the filter and see if it is faulty and could potentially introduce air.  Try to flex it and see if there’s any give which could open a gap – I suspect that’s quite unlikely.

  • #81011

    Brad Clem

    I configured the fuel delivery as Mr Martin suggested and replaced more line while using the pickup from the Honda.  The AX event Sunday was wet, so I did not get a good full throttle testing application.  I never found a “smoking gun”, but it did not exhibit the issue at hand.

    Thank you guys for your help.

  • #81154

    Mike Burrill

    Just out of curosity, what are you guys using to restrict the return line and what inlet needle do you use?  I have used this same set up on an ICC (w/o a restriction) and a Mikuni pump and I have also used a non return Dellorto pump (the one with the 1.5 PSI relief valve)  and both worked  OK for me.

    Mike Burrill -
    Karting Kartel

  • #81446

    Matt Martin



    I just run a zip tie which is pulled tight on the return line.

    What do you mean by inlet needle?  The float valve?


    Brad, get to do anymore testing?

  • #81622

    Brad Clem

    No, I haven’t been able to get out lately.  This weekend or next hopefully.

    I can’t get something off my mind and maybe if I mention it here, there is an easy explanation.  The kart came with a dellorto carb with a straight intake.  In the box of misc parts, I find a spare dellorto and an angled intake that has a larger boot (it fits the pwk 38).  Then on the spare engine is another angled intake and notation on both by that it was modified by Super-Dyne (same on the engine).  So, if you’re keeping count, I have 2-38mm intakes, 2-30mm dellorto carbs and 1-30 mm intake.

    So my thought is that someone kept whatever carbs were being used for this setup and threw in the 2 dellortos.  I don’t think it is normal to use a pwk for a k9b, so what other ~38 mm carb would have been optimal for a modified k9b?

    • #81649

      Matt Martin

      It could be any 38mm carb – PWK, Keihin, Mikuni.  I’m unsure who might do that unless they’re running in an unlimited/modified class.

      Are the Dellorto carbs the VHSH 30?

      What is the setup inside?  Atomizer? Jet?  Needle (and clip position)? idle jet?  Float weight and height?



      I’m not sure which class you run, but my experience is with the KZ/ICC stuff – rules mandate the VHSH 30mm carb from Dellorto.




  • #81631

    John Kwong

    I run a TM K9B and have switched to the short intake.  The TM K9’s that I have seen had a collar that went on the carburator which then fit into the big carb boot that you describe.  The short intake that I have from Green Flag Racing does not use this collar so I guess yours is missing.  I also run mine with no return line or restriction in the main line but I do put a fuel filter just before the carb that acts also as a reservoir for extra fuel.  The karts that I have used with a return line, we used the screw off top from the top of a spark plug inside the return line to create enough resistance so that more fuel pressure will go to the carb instead of the return line to the tank.

  • #81690

    Brad Clem


    The short intake is a GFK.  Is there an advantage to using that vs the other?  I’ve done some driveway testing and it seems to dump fuel into the airbox.  I’ve used the angled intake with the pwk and it works well, but I wondering if its optimal.  You’re using the dellorto pump that doesn’t require a return line?


    I run an open class.  To clarify, I used the PWK in my last test, because I couldn’t get the dellorto to run consistently.  If I run the engine is high rpms in gear on the stand, it does fine.  But if I let off and hit the gas again, it appears there is little fuel in the line.  If I open the choke in time, it won’t die.  I tightened the zip tie and added the plug top as John suggested and it seems better.  My next thought it to move the T closer to the pump as it is currently 3 inches from the carb and may add more reserve fuel.

    I’m using an adjustable main jet to get in the ballpark, but have run through static jets as well.  268 atomizer, 55 idle, 22 needle on clip 2.  I’ve moved the standard float up and down without change.

  • #81923

    John Kwong

    Sorry for the delayed response. My other computer wouldn’t let me log into the forum.

    I found the short intake to add a noticeable amount of power.  I also did the flat top piston and the appropriate head insert.

    The front leaning angle that the short intake puts the carb at is awkward and is probably affecting the float height setting and dumping fuel where it can.

    I am using the round fuel pump that is seen on most Euro shifter motors.  It has two fuel outlets but I just block one and run one fuel line to the carb.


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