She's Lost Her Power, Captain!

Discussion in '2-Stroke Engines' started by klassard, Jan 10, 2009.

  1. klassard

    klassard Member

    I've logged over 1,200 miles on my 80cc engine. This last summer on a ride back home on a hot day, the engine started to bog down while at full speed. I figured it was getting too hot so I stopped for a while. Upon starting back up, it ran normally for a bit, then started bogging down again.

    After that, it ceased to give power after it warmed up. It would start out strong but lose power after only a couple minutes of riding. Strangely though, when I give it gas with the clutch disengaged, it revs fine but no power - this is the part I didn't see in the searches I did on this forum so I figured I'd put it out there.

    I cleaned out the carburetor and changed the spark plug with no success. Any suggestions before I pull the cylinder head off? (I'm not confident I can successfully get the piston rings back in so I'm hoping to leave this as a last resort)

    Last edited by a moderator: Dec 15, 2015

  2. hill climber

    hill climber Member

    sounds like you got the good outa it. check the compression. might have to put rings in or even a cylinder and piston kit. might be a air leakonce it warms up.
  3. MotorMac

    MotorMac Member


    Take the spark plug out and feel with your thumb over the hole if theres any compression. If not then your rings are gone or theres a hole in the piston. If you have good compression then its probably fuel related or theres an air leak,head gasket leak?
  4. fetor56

    fetor56 Guest

    Sounds like a head leak mister.....either that or your matter/anti-matter transformer is cactus.
  5. bluegoatwoods

    bluegoatwoods Well-Known Member

    If it's not the matter/anti-matter transformer, then check your exhaust.

    If it's clogged it can give symptoms similar to what you describe.

    I hope that's it because this is a very easy fix.

    Good luck.
  6. Mountainman

    Mountainman Active Member

    tells you a lot in a short time

    the good old compression test
    tell you a lot in a short time

    if you don't have a compression tester
    you probably know someone who does

    that's not many riding miles logged in
    with only 1,200 miles
    can't see where you got the good out of it ?

    fast question for you klassard -- what % mixture were you using ?

    get that THING back up and ride that THING
    Last edited: Jan 11, 2009
  7. klassard

    klassard Member

    Wow, thanks for the responses!

    I took the muffler off and rode it a bit. It was loud as **** but still bogged down. Unfortunately, I don't know anyone with a compression tool but I figure I might as well pick one up if I'm going to be making a habit of building these things :)

    As for the mix, I'm running 30:1 with Motul 800. I don't know much about the engine. I got it on eBay and it says "Young An" with some chinese characters on the side.

    Anyone know where to get a compression tool?
  8. Mountainman

    Mountainman Active Member

    Harbor Freight has some inexpensive ones

    Sears -- as we know -- one of the best

    take your MB into any auto repair shop
    they may get a kick from checking out your engine
    do a test for next to free

  9. MotorMac

    MotorMac Member

    compression tool?

    You dont need a compression guage for a small 1 cylinder 2 stroke engine! just put your thumb over the spark plug hole and if theres a strong pulse of air then compression is fine. your thumb is a compression tool.
  10. Pablo

    Pablo Motored Bikes Sponsor

    Are your head and intake gaskets in good shape?
  11. Mountainman

    Mountainman Active Member

    takes a good thumb to do that !!

    are we saying here that one can tell the difference

    between 50 psi and 80 psi ??

    takes a good thumb to do that !!

    many here can do the thumb THING
    but also -- many others will not be able to

    a thumb is to be taken much care of -- used often as we ride that THING
  12. fylerc1

    fylerc1 New Member

    Another possibility I've run into, and completely different than these other responses is to adjust your clutch. Mine gets loose once in a while and appears to lose power when it's really just partially slipping. Since you've got so many miles on the beast, it's possible your pads have warn down, requiring a tightening of your butterfly(star) bolt. It's harmless enough to check at least. Remove the screws over the clutch plate, remove the one screw holding the butterfly bolt in place and tighten it up (I use a hammer and a nail set, but whatever works). If this is the problem, it could be fixed in minutes, if not I'm at a loss.
  13. Pablo

    Pablo Motored Bikes Sponsor

    Good pornt on clutch slippage.
  14. klassard

    klassard Member

    I tried my thumb and there seems to be a puff of air but not much. Although, I've never stuck my thumb in an engine before so I'm not sure what constitutes good pressure. On the bright side, there is a Sears and a Harbor Freight nearby.

    Checked the clutch and it is engaging well.

    Thanks again for the responses! I'll grab a compression tester this week and see how that goes.

    Come to think of it, I did notice a little oily stuff around the base of the cooling fins. I wonder if that means the gasket is not sealed.
  15. Pablo

    Pablo Motored Bikes Sponsor

    What are your head nuts torqued to?
  16. hill climber

    hill climber Member

    your thunb has a preasure gauge? were did you get that installed? i need 1 of those. with low compression your motor will run but poorly. get a compresion tester and check it.if the head is leaking you should see black goo coming from the head gasket area.
  17. MotorMac

    MotorMac Member


    Sorry, I guess I need to explain more clearly. By sealing your thumb over the sparkplug hole you can guage if you have good compression or not, when you turn over the engine the pressure pulse from the piston should be strong enough to lift your thumb off for a split second, if it does not lift your thumb off you have an internal ring, head gasket or piston problem. Yes I can gauge the difference between cylinders with my thumb with a multi cylinder engine but I do use a guage for that.
    The thumb test is just to determine if you have compression or not.
    By the way does anyone know what the compression PSI is supposed to be for these small H.T engines?
  18. hill climber

    hill climber Member

    ok, so i just went out to the garage to check the compression on one of my ht's. the motor is a live fast motors 55+cc budget kit. the motor has about 20 miles on it and is stock other than port matching. removed the plug and rested it on the head, insalled compression gauge and rotaited rear tire,turned the motor over about 10 times. throttle was in the idle position. gauge reading was 105psi. gonna go check the other one now.i wanna know.
    checked the other motor, it has had the head milled and a thinner head gasket installed, totaling about .045 inch the compresion read 160psi. this motor has over 1000 miles on it and over 400 since the work was done. 1000 miles, 160 psi and going strong.
    Last edited: Jan 11, 2009
  19. Mountainman

    Mountainman Active Member

    hey MotorMac
    not to get you wrong there
    knew exactly what you were talking about
    the old thumb in the hole test
    you are so right -- good THING to do
    just to get a rough idea

    hey hill climber
    now klassard has someTHING to shot for
    thanks for running out there for us -- checking yours

    hey klassard
    guessing here
    because your engine is not in a compleat failure mode

    if your engine is under 90 psi -- slightly worn and torn
    " " " " " 60 " -- gone baby gone

    if you are 90 psi or above -- not the problem

    ride that THING
  20. klassard

    klassard Member

    Well Pablo, I'm not sure what my nuts are torqued to these days. I think the only time I've ever really torqued my nuts was when I landed wrong off a BMX ramp, but that was a long time ago. In all seriousness though, I don't even have a torque wrench so I'll probably have to pick one up when I get the pressure gauge.

    I do have black goo around the gasket so that might be part of the problem. I'm definitely going to grab a pressure gauge from Harbor Freight though.

    Thanks again for all the help, everybody!