Engine Trouble Open throttle kills power

Discussion in '2-Stroke Engines' started by nashy10, Jul 26, 2013.

  1. nashy10

    nashy10 Member

    i have finally got my 66cc ht installed perfectly and mounted nicely, and i've been breaking it in. As time passed i noticed that i was able to reach higher max speeds (this is normal) but now if i open the throttle as far as i can it will struggle to increase the speed and most of the time just stop powering. The engine doesn't turn off, it just goes slower than it should. This is odd and i cant think of why this happens because the bike now runs faster at a 3/4 throttle?

  2. grinningremlin

    grinningremlin Active Member

    My guess would be an air leak.I've had them develop in fuel lines (bad black hose, ethanol and UV causes cracks you can barely see) fuel tank grommets, same thing.Or a leak around the carb.
  3. wheelbender6

    wheelbender6 Well-Known Member

    Agreed. Air leak. You might add gasket sealer to your intake gasket too.
  4. Purple Haze

    Purple Haze Active Member

    Try raising the needle in the carb if you have the NT carb. This richens the mixture a little, it sounds like you are leaning out. Lowering the clip raises the needle. If it is only leaning out at wide open throttle, you may have to go with a larger jet. There is lots of info on these forums on how to do that.
  5. HeadSmess

    HeadSmess Well-Known Member

    for full throttle, its the main jets too small, theres an airleak somewhere (which will also result in a high idle speed and hard starting) or the crank seals are gone. which usually means hard starting and a bad, erratic idle.

    start with checking the seals, then the leaks, then all thats left is the jet!
  6. jaguar

    jaguar Well-Known Member

    possible leaks:
    1) head leak (hint: stock heads and cylinders need to be planed to match well. lazy chinese *******s didn't do that)
    2) crank seal leak (I have seen new right seals caught on the shaft lip and therefore not sealing correctly)
    3) leak between carb and cylinder
  7. nashy10

    nashy10 Member

    thanks guys i tried misting the engine while idling to check for air leaks, doesnt seem to be any unless theyre in the carb. Will adjust the clip and see if that helps. Also, i was under the impression that these bikes dont idle unless the clutch is pulled, am i correct? ive been riding the thing all along this way, the bike has to run at least 8km/h otherwise it quits (unless clutch is pulled) this is normal, right? if i let go of the clutch while stationary, itd die. also this thing is pretty hard to start, i have to warm it up for about 10-20 mins and open choke to get it running nicely, also noticing the exhaust gets considerably hotter than the engine, and a bit of white smoke. what does all of this mean? Also, the crank seal is something id very much like to check, but i dont know how. also the engine is custom mounted to the bike so taking the engine apart is quite difficult for me. oh, and just to add, the spark plug is also always a singed black, but it runs, and it has crazy vibration at low rpm
  8. HeadSmess

    HeadSmess Well-Known Member

    what does a motorbike or car do if you stop without using the clutch? it stalls.

    standard exhausts are POS. sounds like its blocking up or getting there. pop off its end cap and give it a soak with oven cleaner overnight.

    white or blue smoke?

    crank seals. take magneto cover off, four screws. any oil/fuel in there means seals gone. thats the first one to go as its only skinny.

    take off clutch cover, five screws. look around the smaller gear for oil or fuel sprayed on case. yet to see this one pop ;)

    "singed black" is not a description for a sparkplug. google "how to read a plug".

    loose motor mounts or rubber "vibration stoppers" will increase vibration, especially low speed. make sure everything is TIGHT and dont go thinking rubber will help.

    mounts shouldnt make pulling the engine apart hard unless the installers done something weird and wacky, in which case, shoot them :jester:
  9. nashy10

    nashy10 Member

    checked my plug, it looks fine, nice way between white and black, tiny bit of oil (damp). Checked the magneto, no oil residue or anything. opened the carb filter and it was full of gas, took it apart and cleaned it out. dried it. after putting it back on the engine had a really hard time starting and even running, had to turn in the idle screw. doesnt seem to be any more smoke coming from exhaust, but its substantially loud now. i tightened all the screws on the carb and it seemed to run good, so i took it for a 88min ride (pretty far) and on my way back it started making this loud scraping ish sound like a high pitched metal on metal type sound..still ran in fact actually better than before but now it always makes this noise... did my bearings sieze?
    Last edited: Aug 1, 2013
  10. crassius

    crassius Well-Known Member

    open the clutch cover & drive sprocket cover and look for shiny spots where something was rubbing, also check all along the chain run for spots where the chain might rub
  11. HeadSmess

    HeadSmess Well-Known Member

    more than likely the screw on the crankshaft gear come loose. lol, i had one pop through the cover... teach me not to investigate!

    erm. check the float height in the carb. excess fuel in the filter is a sign the carbs flooding a lil. bit hard to do, really, but anyway. when you pop the carb apart, the litle yshaped thingy that presses on top of the float? bend the tags down slightly. very slightly. sometimes its easier to adjust with the carb off the bike. turn fuel off before pulling the bowl, and fuel level should be 1-4mm under the edge of the bowl. if the bowls overflowing, then the tags need adjusting.
  12. nashy10

    nashy10 Member

    okay, found what was making the noise. I took the clutch cover off and the flower nut was all bent out towards the clutch cover, and there were multiple scrapes on the inside of the cover. i have included some pictures to show you what i mean. Other than this, i took apart the entire carb, cleaned everything up and extensively cleaned it out, and set the mixture to one setting richer. After all of this, the riding was absolutely amazing, never had so much power with this bike! but sadly, after a while of riding the grinding noise came back. i might also add that my clutch cover is slightly cracked and not a flat even surface as it came slightly warped :/ it doesnt seem to affect performance, but its really damn loud. also, now i get a lot of white smoke at lower rpm but i dont think this is a big deal, is it? 20130804_145403.jpg 20130804_145346.jpg
  13. HeadSmess

    HeadSmess Well-Known Member

    unusual...wheres the crank nut?!

    get one ;)

    um. but that wear mark from the clutch...its not going to kill anything but the cover. hopefully.

    probably been machined a few mm undersize.

    few gaskets might help. new cover will definitely.

    never seen one do it before...
  14. crassius

    crassius Well-Known Member

    what he said
  15. nashy10

    nashy10 Member

    i guess a new cover would help. yes i have the nut its just off in that picture. Also, after richening the mixture it smokes white frequently, and the plug gets really hot. plug colour is black, dry.. does this mean anything
  16. HeadSmess

    HeadSmess Well-Known Member

    2strokes burn oil and make smoke.

    sparkplugs get hot. black is a sign of too cold a plug or too rich a mixture. experience tells which.


    a 2stroke will hardly ever look "normal". dry,black/tan/grey and or deposits is "normal". wet is bad. as is anything else.
  17. nashy10

    nashy10 Member

    it looks just like the "Dry" plug as you have pictured. i assume running it like this wont be bad for performance?