Home Forums Road Racing SHIFTER CARB QUESTION

This topic contains 4 replies, has 3 voices, and was last updated by  Timothy Strawkas 7 months, 3 weeks ago.

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  • #79680

    Timothy Strawkas
    Participant

    What would be more plausible. At Gateway last year I had A reoccurring problem. After 2 laps of running good and strong. My PJ non pump around carb would bog/give out (actually died 2 times ,once was able to get it to fire right before it stalled once) all together coming out of the oval turn 4 and/or out of turn one. Never acting up on the right hand 180 corner or the adjacent left hander leading onto the oval. It was pretty consistent in this problem.   I had always thought it was the fuel pump the day of and didn’t have A spare. I took it back to the sprint track I normally race at without changing anything and ran 40 + laps with no problems at full speed. The carb had one pump and A tee in the pressure line with A restrictor. I’ve run it at the sprint track like this for 2 years. So I’m still not convinced it was the fuel pump but looking for some theories. My overflow breather tubes were set up like A motocross bike with them going up and looping to the other, with slits in them. I kind of think they may of been flooding the carb with them in this position from the constant gforces? With out testing I’m not going to know for sure but looking for some more thinking on this. Thanks

    #79886

    Robert Lawson
    Participant

    Tim,

    Just from your description it sounds like your float level is too low.

    I have had experience with the PJ and the PWM Keihin carburators. They will run just fine while puking fuel out from a high float level. Your competitors may not like you though!

    The PJ needed the inlet needle and seat changed (machined out and replaced) to work properly on a RR track. Even then, the float level was extremely critical and very sensitive when it came to cornering at any speed.

    The PWM is far more user friendly. Pump/fuel line set-up is straight forward too. (see below)

    If you are using a round Mikuni pump with dual outlets I would suggest running one line straight to your carb, and the other as an unrestricted return back to your tank. This is a standard starting set up. (50/50) *** -> Pulse line as short as possible!

    Set your floats (bowl off, carb upside down) so the fuel shuts off when the float seam is just past that seal/gasket surface on the carb body. This will be a little on the high side but a safe starting point.  This is easy to do, put a piece of fuel line on the carb, turn it upside down, blow into fuel line and work the float arm with your finger, finding the point where the fuel (air) will shut off. Do it a few times and adjust it to be just beyond view hidden by the carb body at that gasket surface.

    Float level on the Keihin is crucial and will change transporting your kart to and from the track. Once you get it right you may not have to check or adjust it everytime but it is something you will have to manage. I would keep multiple float arm assemblies preset to different levels and just swap them out instead of adjusting them all the time.

    I am not an advocate of the “pump around”, never used one and never really needed to. It just takes some testing to figure out the fuel line configuration that suit your fuel system. Not sure you will get that PJ to work consistantly on a RR track but I wish you the best of luck!

    Can’t believe there were over 130 views and no one bothered to throw something at you here. Not sure where you are located but we are testing all day at Grattan Raceway in Western MI  April 8th if you want to work it out. Plenty of CIK shifter guys will be there to assist you.

    Again, good luck!

    RPM

    #79913

    Jim White
    Participant

    Make sure your fuel pick up on the tank is fresh and flexible. Could be g loading on those corners is causing the fuel to slosh and the pick up not following it. Especially if it’s only turns in one direction.

    Been there done that!

    #79916

    Robert Lawson
    Participant

    Good Point Jim, I forgot that!

    Maybe not as critical at full fuel load but easily overlooked none the less.

    #79985

    Timothy Strawkas
    Participant

    Thanks guys. The PJ series is just what I had to work with. May just have to change it over. I’m pretty good with carb floats, I grew up rebuilding friends motorcycle carbs, holley, quadrajets, yadda yadda. The pick up line is new and long. I’m just leaning to the carb itself. Your the second person that has mentioned the PJ just isn’t friendly to road racing. The day of the race we tried 2 different pump line routes and neither worked, deltro and single round system. I bought A PMW at A swap meet over the winter to give A try. I’m really surprised that road racing is not more “chatted about ” o this forum. It is A lot of fun. I only got 7-8 laps in last year and still had A blast.

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