Engine Trouble motor knocking/no torque

Discussion in '2-Stroke Engines' started by namefail, Feb 24, 2013.

  1. namefail

    namefail New Member

    motors 3 tanks in and has gotten progressively worse. works well on straight aways and slight inclines. is 4 stroking i think but im not sure how to exactly determine that. but i live up a pretty big hill and ive had other bikes that climb it so i know its not that bad. but this guy just loses all power and knocks pretty bad. has a cent clutch on it. might be losing power that way. i dunno any help would be swell
     

  2. Fabian

    Fabian Well-Known Member

    If it's a fresh engine, start by ditching the standard CDI and replace it with a Jaguar CDI. The knocking sound could be a number of things but i doubt the centrifugal clutch is the problem.
    When new the manual clutch will need time to bed itself in. I would look at tightening up the flower nut on the manual clutch by 2 index points, to get a little more clamping force on the pressure plate.

    How hard have you revved the engine?
    Have you gone downhill at speed without pulling in the clutch lever?
    Is the air filter securely tightened?
    Do you have any air leaks?
    Are you running a cylinder head gasket?
    Does the engine use 6mm or 8mm studs?
    Is the cylinder head centrally located on the cylinder?
    Have you disassembled and reassembled any engine parts?
    What octane fuel are you using?
    Are you adding any oil to the fuel?
    Is the carburettor using standard jetting?
    What type of spark plug is installed in the engine?
     
  3. jaguar

    jaguar Well-Known Member

    Jet it leaner
     
  4. namefail

    namefail New Member

    i was thinking it might be a blown head gasket but i havent noticed any air/oil leaks. how do you jet it leaner? ill look it up

    i might have revved the engine to high at first trying to climb hills. i use ngk bh6, 91 octane/oil with stabilizer.
     
  5. jaguar

    jaguar Well-Known Member

    For leaner running at mid throttle you just lower the needle in the carb. For leaner full throttle running you can replace the main jet or solder it shut and use a micro drill bit to make a new and smaller hole. Click onto my signature link to read more.
     
  6. Fabian

    Fabian Well-Known Member

    What is your final drive ratio?
    What is your wheel diameter?
    What is the fastest speed you've seen when going downhill?
     
  7. V 35

    V 35 Member

    My first build ... Bike ran ok, was very dissapointed in total lack of torque, thought concept of being able to pedal downright silly, as
    bike was very hard to pedal . Re-adjusted drive chain [ little too tight ] big difference in pedaling . My flower nut was one click too tight,
    that said, the bike now pedaled OK [ not great ] and the engine now revved up easier. Torque gradually improved as clutch broke in, after a cable adjustment, bike was now a satisfying ride. Lift rear wheel with sparkplug removed [ easy turning = no compression ] and check drive
    for ease of movement. If bike is stiff, you'll have no torque.
     
  8. namefail

    namefail New Member

    thanks jaguar. i moved the clip down to the the leanest setting and it pulls alot better. handles the med ranged hills without issue. the big hill it pulls well enough but at open throttle it still knocks and decelerates but ill work on that. might order a new main jet. thanks again man and the site you put together is pretty intense. good stuff!
     
  9. namefail

    namefail New Member

    its 46 tooth sprocket 26inch tire 2.125.

    with the leaner setting its weaker pulling from a dead stop but has more torque on incline which is ideal. it just basically died and over heated before i changed the setting
     
  10. Fabian

    Fabian Well-Known Member

    What is the fastest speed you have seen going downhill using the new engine?
     
  11. Fabian

    Fabian Well-Known Member

    because if you've gone 30 mph on your final drive ratio, your engine will have revved to 7,400 rpm, and that's after i've double checked the maths.

    If that's the case, it's time for a new engine because the connecting rod bearings (most likely the big end bearing) will have taken a huge beating, and no amount of jetting will fix that!
     
  12. namefail

    namefail New Member

    fabian i usually coast down long hills but ive been varying my speeds. nothing over 20 mainly because i drive into downtown pittsburgh daily and dont want to get crushed by a car. drivers here dont give much room for bikes.

    on a back road flat i went up to high 20s but not a sure number i dont have a spedo on this bike just guesstimating
     
  13. Fabian

    Fabian Well-Known Member

    Either way high 20's or low 30's means you will need a new engine, as these engines have been upgraded to a crowded big end needle roller connecting rod design, which is great for load bearing capacity and resistance to detonation and longer engine life, but it's less tolerant of high rpm than a caged needle roller bearing design.

    From my experience with fixing engines for other people, it's rpms over 5,000 that seems to significantly reduce engine life and rpms over 6,000 just kills the connecting rod bearings in quick fashion.

    Hight 20's with your final drive ratio will still give a number close to 7,000 rpm, which means your connecting rod bearings have been irreparably damaged.
    The best way to fix the knocking problem is to purchase a replacement engine, and to keep rpms below 5,000; and ideally below 4,000 for extended engine life. One excellent method to achieve this is to install a reed valve intake, boosting low and midrange torque; enabling you to run taller gearing and using less rpm for the same road speed, especially on a fixed gearing final drive system, which is the least flexible gearing method you would want to be use.

    By far, fitting a SickBikeParts shift kit will solve all of your engine over speed issues; keeping the engine in it's torque butter zone for whatever road speed you are travelling at.
     
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