Engine Trouble SkyHawk GT5A 66cc Engine Severe sudden power loss

Discussion in '2-Stroke Engines' started by P3_Takuto, Apr 14, 2015.

  1. P3_Takuto

    P3_Takuto New Member

    I have a SkyHawk GT5A 66cc engine that has at least 300km on it. After replacing the stock carb with a CNS high performance carb and boost bothe I took it out for a 10k ride, all was well. The next day I go to start up the engine. It had a much harder time starting and when started it barely revved high enough to get into gear even at full throttle let alone idle and the engine was shaking more erratically than it used to, I thought, probably something with the carb, so I check for any blockage and drained it. No problems. I checked the choke and throttle, both perfect. I checked all my connections to the carb and all was good. So I tighten all the mounting bolts and such, no issues there either, so i checked for exhaust blockage, no blockage other than the exhaust is a little lighter. but I'm still stumped, could it be internal damage? If I block the fuel source it will rev almost as much as it should but let the fuel flow again it loses almost all power, could it be a head or gasket issue? I don't know I've tried everything but I honestly don't know what could have caused it from perfect functionality to barely running.
     

  2. crassius

    crassius Well-Known Member

    first thing to do is put the old carb back on & see if that helps
     
  3. KCvale

    KCvale Motorized Bicycle Vendor

    If you forgot to turn off your fuel valve your new carb could have overfilled and poured raw fuel into the crankcase.

    Pull out your plug.
    With the fuel off and no throttle pedal your bike up the street and back with the clutch released to blow out any raw fuel in the crankcase.
    It's amazing how many times this simple fix works.
     
  4. P3_Takuto

    P3_Takuto New Member

    Alright, ive tried running without the spark plug with no throttle or gas and no luck with that. I've tried using the stock NT carb and it runs without any problems so it must be the CNS carb. I've played around with the air/fuel screw but it proves to be useless since no matter what setting its on it still acts the same even with the screw removed. I've drained the carb completely and no improvement. It's getting to the point that I have to use full throttle to keep it idling. I've checked my fuel/oil ratios and I'm at 1:25 which I normally run, something must be up with the carb but what could it be..
     
  5. Roy K

    Roy K New Member

    I had the same problem with mine, fixed it by changing to a smaller jet and by running a hotter spark plug.
     
  6. crassius

    crassius Well-Known Member

    full throttle to idle usually means you're too rich - I tell my customers that if ports & exhaust are not seriously modified, then a CNS just will never work right - too large a venturi to respond smoothly thru th whole throttle range

    when the NT works, run it
     
  7. P3_Takuto

    P3_Takuto New Member

    I'll try finding a smaller jet, how small a jet would you recomend? Also until I can fix the carb I'll be sticking to the NT carb. It runs hot but it's better than nothing
     
  8. Roy K

    Roy K New Member

    The one my carb came with was a .70 and I changed it to a .66.
     
  9. crassius

    crassius Well-Known Member

    mufflers vary a lot in flow rate even when they look the same on the outside - same with flow thru engine ports due to slight diffs in machining & placement - I'd recommend soldering up the jet, then trying several diff sizes of micro drills till you find one that works well - that makes it easy to resolder & try another size
     
  10. KCvale

    KCvale Motorized Bicycle Vendor

    One other note on CNS carbs is they tend to leak air at the intake, the new ones should have a rubber seal as wide as the split the attachment bolt goes through, if not gasket sealer works to fill that groove.
     
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