Strange noise preventing power

Discussion in '2-Stroke Engines' started by Chriskelly, Aug 17, 2016.

  1. Chriskelly

    Chriskelly New Member

    Really scratching my head,when pulling the throttle to speed up I get to about 22mph and the normal whine the engine makes turns into what I can only describe as a air flapping very fast noise,it jumps between this and the normal whine of the engine speeding up noise every few seconds! I'm thinking either my Cdi is no use at high speed or some issue with piston skirt clearance? Please help also when it is jumping between the two noises when it returns to the normal noise it speeds up for a second.
     

  2. jaguar

    jaguar Well-Known Member

    air flapping noise at speed does not sound like the engine. sounds like your coat tail
     
  3. Chriskelly

    Chriskelly New Member

    Definitely not my coat! It only does it at high rpm under load,it sounds like pressure waves or something,this engine struggles to hit 27 mph on the flat
     
  4. jaguar

    jaguar Well-Known Member

    probably 4 stroking
    click on my signature link and read about it
     
    Frankfort MB's likes this.
  5. CrazyDan

    CrazyDan Member

    Are your head bolts coming loose? Any other bolts loose elsewhere? These 2 smokers require regular maintenance or else things go bad real fast. Each time before riding check your head, exhaust and mounting bolts minimum. I don't trust 2 strokes, they'll fall apart mid-ride. One way to slow their self-destruction would be to use blue lock tight on every bolt. Make sure the chain and sprocket are lined up, and the engine mounts are solid. This all will reduce vibration (which will limit your top rpm), without modification to the flywheel or piston, but as I'm very sure Jaguar will explain to you, lowering the weight of moving parts and proper balance will make vibration all but disappear. His CDIs are very good from what I've read at further reducing vibration by changing the timing at higher rpms. I'm not the best voice for giving advice to make 2 strokes purr, I owned one and ran to 4 strokes, too busy sometimes to constantly maintain them lil vibrators.
     
  6. Frankfort MB's

    Frankfort MB's Well-Known Member

    I'm with Jag it sounds like your running a rich fuel mixture causing your bike to four stroke
     
  7. Chriskelly

    Chriskelly New Member

    Right guys,ive moved the throttle pin clip to the end groove I believe this is the leanest position,has had no effect on performance or the noise,ive also tried moving the choke with no result,any other suggestions? Is it possible to upload a audio file here as probably best to hear it as it's a hard thing to explain.
     
  8. LRSimons

    LRSimons Member

    Pull off the airbox/ filter and take it for a spin. The stock one is generally restrictive enough to richen the mixture. With it off you will at least be able to see if you're going in the right direction.

    If it does get better but not solved, you'll need a smaller jet. Either buy one or fill yours with solder and drill a smaller hole.

    Or start modifying for power. The fuel demand increases with performance increases. Probably best to get your engine running smoothly stock though.


    Logan
     
  9. jaguar

    jaguar Well-Known Member

    they all come with too big a main jet hole. they all need a smaller jet size.
    moving the needle doesn't affect the mixture at full throttle, only the main jet does.
    and yes if the filter is restrictive then it needs to be replaced with a less restrictive one. but that won't fix the main jet problem.
     
  10. crassius

    crassius Well-Known Member

    you might try loosening the muffler just a bit (maybe 1/8in gap) to see if something came loose inside it
     
  11. Chriskelly

    Chriskelly New Member

    I've got the air filter of until I get a chance to modify the intake as my frame is small and won't fit,took the bike to work this morning and had trouble with it bogging out when I pulled the throttle but after tweaking the choke it started to go properly bit still with the noise,the noise did stop for the last minute of my ride so will update later on my way home to see what the situation is
     
  12. Chriskelly

    Chriskelly New Member

    Also I have cut my baffle and taken 1ml of the circumference of the muffler outlet pipe on cap
     
  13. Chriskelly

    Chriskelly New Member

    Update! On my way home today the noise/four-stroking was still there for about five minutes then stopped once engine got hot! Is that four-stroking?
     
  14. jaguar

    jaguar Well-Known Member

    a cold engine likes a rich mixture more than a hot engine
     
  15. zippinaround

    zippinaround Active Member

    by air flapping do you mean like a popping noise? if it sounds like air coming from somewhere it probably is the head gasket , when the engine gets hot the metal expands closing the gap? just my thoughts if it is the head you should see an oil mark where its blowing out
     
  16. Chriskelly

    Chriskelly New Member

    Hmm,thats odd as I was sure I was running rich but it does seem to be sounding and performing better now once it's been run for five minutes and engine is warmed up,i have another carb in the shed going to try that as a comparison to see if it runs better or worse with the jets on that one
     
  17. Chriskelly

    Chriskelly New Member

    It's definitely not the head,i had a bolt snap on my first after over tightening due to in experience and rode it for days before I got the new parts,had to for getting to work lol,the new engine has just had the head changed from a punch to a slant head for better frame clearance and is perfectly sealed,although I do plan on using a thinner gasket at some stage
     
  18. Chriskelly

    Chriskelly New Member

    Tried the other carb I have! It bogged out and died every time I started it,so back to the old carb
     
  19. Chriskelly

    Chriskelly New Member

    Update! I swapped the jets as one was shorter so my theory was the needle would be more restrictive, worked a treat no four-stroking at full throttle,bike is slightly slower at acceleration but hits higher top speeds (37mph) on my short test run and sounds much better next step is to re shape the intake so I can fit my carb cover on
     
  20. CrazyDan

    CrazyDan Member

    Make sure after each adjustment you make to the engine to tear it around the block and come hauling butt up to your house, killing it while at wide open throttle. Then check your sparkplug to see how your engine is running. White=lean, black=rich, brown=just right. I prefer a darker brown to a lighter brown, slightly rich runs a little cooler with not much power loss. Slightly lean can be snappier but tends to run hotter. Nice to see you've solved the issue ;).
     
Loading...