Home Forums Shifter Karts Modded CR80 with high RPM flutter

This topic contains 10 replies, has 4 voices, and was last updated by  Gary Smith 5 years, 1 month ago.

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  • #5085

    Gary Smith
    Participant

    I have this CR80 cylinder that has been ported to the max, the transfer ports are big enough to stick your finger thru, I  have also ported the cases to match these transfer ports. The problem I am having is at about 10,000 -11,000 rpm I am having a flutter, the motor stumbles, seems to clean out and continue to climb in rpm. Sometimes the motor runs clean for 5 laps or so then goes back to this flutter. I have tried leaning the main, which made it worse, richen the main and back to square one.  I started out with #40 pilot, #200 main, went to #195 main, then to #210 main, all with the same effect, the plug looks dark. I am running low tension reeds, they have always worked for me in the past with stock motors.

    Would high tension reeds work better?

  • #5115

    William Martin
    Participant

    It’s probably not the reeds. My first “GUESS” is that your transfers are too big to get the flow velocity needed. It seems counter-intuitive, but ports can be too big…

    -bill

     

  • #5163

    Gary Smith
    Participant

    This cylinder I have came with a motor I bought 5 yrs ago, I thought , what the heck, put a piston in it and see what it does. I did not bother to put new reeds in it. Upon inspection of the reeds, one of them has small break forming on the top edge. When I bought this motor, it came with a set of reeds with a stiffener, I assume these would be high tension reeds. The next time I go out, I will try these reeds, see if it makes a difference, I have an extra reed cage that I have already mounted a set of new low tension reeds.

    Gary

    #55 Honda CR80

  • #5215

    William Martin
    Participant

    This cylinder I have came with a motor I bought 5 yrs ago, I thought , what the heck, put a piston in it and see what it does. I did not bother to put new reeds in it. Upon inspection of the reeds, one of them has small break forming on the top edge. When I bought this motor, it came with a set of reeds with a stiffener, I assume these would be high tension reeds. The next time I go out, I will try these reeds, see if it makes a difference, I have an extra reed cage that I have already mounted a set of new low tension reeds. Gary #55 Honda CR80

    Sounds like a plan…good luck.

    -bill

     

  • #5381

    Broque Ward
    Participant

    make sure your ground is good. that can cause that.

    whats your spark plug gap?   too wide of a gap will cause that go down .002 thou until it stops or move to the next trouble shoot.

    you need to test your cdi, coil and stator for the correct readings.
    If you checked the two above then you need to test, your breakup can be caused by one of those or all of the electrical components going bad.

    I doubt broken reeds would cause an issue at WOT.

     

     

  • #5406

    Gary Smith
    Participant

    Just checked my wiring, all connections good, with good grounds.

    Plug gap .022, spec .024-.028

    The motor doesn’t always  break up under WOT, it’s just this RPM range of 10,000-11,000 , it happens sometimes feathering throttle out of corner prior to nailing it. The reeds in the motor had 30 hrs on them, they were damaged, I have changed them with ones that came with cylinder,  I will try them out and see if the problem persists.

    If the problem continues, I will check out the electronics, but I doubt if that is the problem, it worked fine before. (every mechanic loves that line) lmao!

    I have a kill switch, like before, it worked fine before, I will disconnect it see if it makes any difference.

    The motor has run a few what I would call clean laps without breaking up, and when it does, it runs like a raped ape, lots of midrange and top end. I find myself over revving between shifts at 13,500, motor still pulling.

    Gary

    #55 Honda CR80

     

  • #5412

    Broque Ward
    Participant

    hmmm, id still check with your voltmeter.  to be sure…

     

     

    whats the compression on the motor? and how many hours on the top end?

  • #5417

    Gary Smith
    Participant

    1st time out with top end, new seals, 30 hrs on crank.

    At the end of break in, when I started picking up RPM’s, I first noticed this problem, never experienced anything like this before, never ran this cylinder before. I have had this cylinder for 5 yrs and finally had the juevos to put this massively ported cylinder on a motor. I don’t know if there is a problem with the cylinder and that is why it came as an extra in a “motor package”.

    One thing I forgot to mention, the cylinder has an “o” ringed head,  I am experiencing a minor coolant leak on the exterior between the cylinder and head, with no coolant loss and no coolant in combustion chamber.

    Gary

    #55 Honda CR80

  • #18275

    Gary Smith
    Participant

    UPDATE:

    During the past 5 months, have tried many things to figure this out, turns out it must be the black box. It runs good some times, and other times runs like crap. I put on an old Vortex ignition box and ran great, then the cylinder cracked along the intake port, put on my other cylinder, ran great, changed back to the old black box, ran great, changed complete motor and after break-in, runs like crap again. The same thing, around 10,000 rpm it starts to flutter. New motor has different stator and pick-up, the only thing that is the same is the black box and coil. Have 2 spare black boxes, I feel confident changing that black box will fix the problem.

    Gary

    #55 Honda CR80

  • #18352

    Greg Lindahl
    Participant

    That broken cylinder is likely from those ports large enough to put your finger through.

  • #18375

    Gary Smith
    Participant

    Greg I believe you are absolutely correct about the cracking along the intake port, the cylinder had been welded on 1 side already, cracked thru that weld and started cracking on the other side of the cylinder as well. Like I said, this ported cylinder was an extra offered in the purchase of “motor package with extras”. I put this cylinder on to see what it would do, unfortunately the ignition took a dump the same time I put this cylinder on. I was quite impressed with the performance gain, 1/2 second a lap and lots of rpms.

    Gary

    #55 Honda CR80

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