Please help

Discussion in '2-Stroke Engines' started by Jcarr, Sep 9, 2014.

  1. Jcarr

    Jcarr New Member

    The motor is a pk 80. Ok so I really need to get this fixed due to this being my only source of transportation. Problem I'm having is motor runs fine at idle and low rpm but as soon as I give it a lot of throttle it just kind of stays at the same speed and seems like it's being limited. I put a new cdi and magneto coil in last week and everything ran great. It doesn't even seem like it wants to go faster. I've tried 3 ngk b6hs plugs. I've moved the clip one notch in either direction. I drilled holes in the baffle and I made sure the air filter was clean but still no change, almost seems to be getting slower top speed. I double checked my electrical connections. Im about 3 1/2 full tanks of gas through the motor now. Do you think it's time to change my oil/gas mixture? I'm stumped someone please help
     

  2. jaguar

    jaguar Well-Known Member

    without details how are we to help you?
    If you say that 27mph is the max then we will laugh and say that is normal.
    If you say that 20mph is the max then we'll know you have a problem.
    What is your elevation?
    Does it "waahhh" when you open the throttle or sputter or run rough?
    what size tire do you have?
    what size rear sprocket?
    Does it run faster with the throttle half way engaged?
    Have you checked the float height inside the float bowl?
    Have you planed the head and cylinder top to make sure they are flat and therefore getting a moderately good seal (since compression loss causes power loss)? (click my link to read more)
    Have you blown through the air filter to see if it feels restrictive to air flow?
     
  3. Fabian

    Fabian Well-Known Member

    The throttle slide needle has no virtually effect from around 1/2 throttle to wide open throttle.

    I would be looking at the fuel filter and then looking to see if you have proper fuel flow through the rest of the carburettor and when assembling the carburettor on the intake pipe, make sure to use an o-ring that sits against the lip inside the carburettor bore, where the carburettor will then sit against the face of the intake pipe.
     
  4. Jcarr

    Jcarr New Member

    I'm averaging a max of about 15 mph right now. It was originally maxing at about 30 mph. So huge power loss. Elevation is nt much at all in Pennsylvania. I'd say 500-1000 ft above sea level. It more or less runs rough, not really sure how to describe, the rpms just don't go up after a certain point. 29inch tire with the original sprocket that came with my kit, I believe it's a 44 tooth. It runs great up to 15 mph and just dosent want to go any faster. I pulled the carb apart and cleaned it well everything seems to be in order in there. As far as planing the head no I haven't done that', like I said it was running fine until 2 days ago. Everything is torqued to spec. Air flow is good, I'm really at a loss right now on what to do next.
     
  5. Fabian

    Fabian Well-Known Member

    It took me 2 years to get my bike to run reliably, and it was a painful experience getting it to give me the kind of reliability i demanded.

    These engines (although they look simple) are a test of your perseverance and mental toughness, for they just keep throwing problems at you.
    Having said that, i have gone through the pain and my bike is now a pillar of reliability, but it has cost me two relationships and a lot of money.
     
  6. Jcarr

    Jcarr New Member

    I'm very familiar with 2stroke motors, I grew up with blasters, banshees, and more dirtbikes than I can count. That being said I don't think I've ever been soo frustrated working on one. I forgot one detail... Seat post motor mount snapped the bolts, could that be the verdict? I just now replaced the studs and have it secure once again. A wee bit late for a test ride though
     
  7. Jcarr

    Jcarr New Member

    I have a no ring on and carb is snug. I have proper fuel flow to the carb, how do I check the carb to see if fuel is flowing properly in it? Again this is why I'm so confused about the problem,
     
  8. crassius

    crassius Well-Known Member

    a loose motor mount could do that - otherwise a speed drop like yours usually means the cases are not tight enough to seal or your crank seals are blown out
     
  9. dougsr.874

    dougsr.874 Active Member

    What carb do you have??? If its a CNS, then throw it away and put on the standard NT.....they're not fancy but they work...
     
  10. Jcarr

    Jcarr New Member

    I'm pretty sure it's an nt. it's marked speed on the side
     
  11. KCvale

    KCvale Motorized Bicycle Vendor

    It ran faster, now it don't, did you check your throttle cable?
    Your cable stops at both ends could have come loose and it's unable to pull the throttle all the open.

    Simple test.
    Is there slack at the throttle?

    Pull off the air cleaner and look in the carb at WOT and see if it goes up all the way.
    To fix just adjust the twisters at each end to take out any cable slack and tighten the lockers against them so they don't loosen up.

    You don't mention what break-in mix you use.
    3 1/2 tanks is plenty, you can run 32:1 now.

    Also, the best plug is an NGK 5944 (BPR7HIX) Iridium, you will feel the difference.
     
  12. Jcarr

    Jcarr New Member

    Yeah it ran much faster. I'm wondering it it's the mix that's making it run bad now that it's broken in. The slide moves all the way up . I was using 16-1. I'm currently running an ngk b6hs but will definitely get the 5944
     
  13. Jcarr

    Jcarr New Member

    From personal experience with other 2 stroke machines I think it's a carb problem. Almost seems to be getting too much fuel but a plug chop is showing like a dark chocolate color with minimal oil, as if it's firing 50-75% of the time
     
  14. Jcarr

    Jcarr New Member

    Ok it's definitely a carb problem. I moved the needle to the leanest position and I'm running about 20 mph vs 15 mph. Gained a little more as you can see but as I open the throttle all the way it still seems to be limited/ minor rough ride. Does anybody have a tutorial with pictures on soldering and re drilling the main jet. Or should I run the new 32-1 to see if that clears things up?
     
  15. Jcarr

    Jcarr New Member

    Ok update. With the needle set to the leanest position the bike will once again enter high rpms only on down hill. Flat and any sort up grade up it just won't enter high rpms. Could this be a clogged exhaust not allowing airflow/ restricting motor output under stress?
     
  16. Jcarr

    Jcarr New Member

    It seems to be doing the wahh like you said. I set needle to leanest position and the bike will enter high rpms going downhill. And flat or upgrade and the motor won't enter high rpms. Could it be due to a clogged exhaust restricting motor output under stress? I pulled it off and the inlet dosent look to have a build up. I did read about a catalytic converter, I pulled the cap off and can't see one.
     
  17. crassius

    crassius Well-Known Member

    I'd switch to 32:1 before I started changing things - if that doesn't help, I'd be looking for what changed since it last ran well.
     
  18. Jcarr

    Jcarr New Member

    I'm going to switch to 32:1 when I finish this 1/4 gallon. I have my power back. Took the head off and noticed some oil on the headgasket, added some sea lent when I put it back together and made sure it was torqued at 12 lbs. I guess around the one stud it loosened up just a hair and thus I lost compression at a higher rpm. Fingers crossed that's all it was. Now it's time to richen the needle a bit as I can tell the leanest position is running too lean
     
  19. crassius

    crassius Well-Known Member

    told you it was a sealing problem : )
     
    Jcarr likes this.
  20. Jcarr

    Jcarr New Member

    Yeah I guess I thought the motor would rev out from being lean like my banshee and blaster did from a bad seal. This motor did the opposite
     
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