Engine Trouble Loud pop noise, dead engine, acceleration w/o throttle

Discussion in '2-Stroke Engines' started by CarbonBikes, Oct 16, 2013.

  1. CarbonBikes

    CarbonBikes New Member

    So I posted a problem a while back that I was getting acceleration without using the throttle and it turned out the throttle cord was pinched (that was on a friends bike). Everyone kept telling me that I had an air leak. Now, I know what an air leak is and kind of how to fix it, but everyone kept saying about adjusting the CNS carburetor because it was running too lean? This I don't know how to do. I kept reading that there's a needle to make it more or less lean. So I was wondering if someone could point me in the right direction for a CNS V3 Racing Carb lean setting- unless I don't need it because I'm not sure what the problem is.

    And I haven't tried the choke method so I'm not sure if it's an air leak, but I get about 25-30 mph W/O any throttle at all. When I try to put the clutch in for idle, it revs way, WAY too high. The only way I feel like I'm not going to blow up is to kill it then put the clutch in.

    -Before above problem-

    My bike was running "fine" getting me from place to place w/o too much problems. It was only running at about 15 mph compared to the 25 I normally got. So I decided to take the engine apart to see if I could figure out and problems. I drained the engine, cleaned up the carburetor and got everything remounted (after noticing no problems). The bike ran really well (just like it used to before I started having all these problems) then a loud pop noise and the engine died right away. This was sudden too, no weird sounds then a pop; I was just riding and a pop. So obviously, I got off my bike to figure out WTF happened. Couldn't see any visible damage, nothing was leaking, dripping, smoking, etc. Once the engine cooled off I took it apart again to check the piston rings, crank shaft, all the housing, electrical, everything was normal. I still don't know where that noise came from.

    Well I let it sit for a few days and early today I figured I go and try to fix it. Well as it turns out, it still wasn't working. I took it for a ride to try and start the engine (I enriched the oil mixture to a 32:1 ratio, switched out my exhaust for the original one) It kept trying to start it sounded like it would fire once, humm for a bit, then fire a few times consecutively, humm for a bit (all while I was pedaling, repeated this process x8). So on the eighth attempt, i hear another loud pop noise but this time the engine starts after the pop noise. After that it has some extremely hard times trying to stay on, but it accelerated a little bit, it idled; it would almost die then rev back up, almost die (repeat). I let it idle for a few minutes till it was idling a little more steady. It was working pretty good but then I get so far I hear more engine popping and it almost dies, instead losing all of its' power.

    So I felt like it was a miss-fire issue or a fouled spark plug. I switch the spark plug out and now I have this acceleration without throttle problem. When I do give it throttle it sounds like I'm about to start flying. When I put the clutch in to try and idle it sounds like the engines trying to idle as fast as a car's engine.

    Is this an air leak or do I have some other issue?

  2. keatonx

    keatonx Member

    sounds like a lean mixture caused by an air leak. The popping could be backfires coming from the intake. I don't know what makes flames want to come into the intake from an air leak, but this always happens to me when a cheap plastic weed eater intake manifold cracks. My 2 stroke lawnmower bike also has a HORRIBLE habit of having a huge intake/crankcase explosion that blows the carb and reed block right off of the engine, whenever it gets an air leak. Sounds like a gunshot and destroys the intake peices (bends mounts, cranks manifold, etc.) Thats an extreme case tho:D

    To check if it's an air leak, get an aerosol can of fogging oil, wd40, etc., and spray it all over the intake pipe, especially where it bolts to the engine/carb while the engine is running at "idle" (if it's revving, just let it rev, it'll only be running for 30 seconds or so so won't hurt it). If it starts running different (slows down, etc), then you have an air leak.
  3. keatonx

    keatonx Member

    Also, if it's a big air leak, then you can ride it a little bit to get it warm, then shut it down. Then SLOWLY push the bike so that the engine is SLOWLY turning over. You might be able to see white smoke leaking from the intake pipe area, indicating an obvious air leak. But if you don't see anything it could still be an air leak, this is just a trick that will sometimes work.
  4. CarbonBikes

    CarbonBikes New Member

    I went and bought a cigar and while the engine was running put the cigar underneath it so the smoke would come up past the engine- nothing went into the engine around the head or intake. I am noticing though (this being the first time I rode with shorts on) that I'm getting burned a lot by little hot black liquid. I think it's oil but I'm not sure. It just sprays out every now and then from somewhere. I think it might be the exhaust.
  5. tom-fishing

    tom-fishing Member

    Think I would be checking my head gasket also.
  6. Uncle B

    Uncle B New Member

    Are you using the stock CDI?
  7. HeadSmess

    HeadSmess Well-Known Member

    head gasket. check it, tighten studs.

    the black oil is either from yes, the exhaust gasket, which is nothing if you can live with the mess, or the head gasket again. thats an issue that does need attention.

    make sure the slide in the carb is around the right way.

    make sure idle screw is out around 2.5 turns. its the only screw on the thing.

    the needle does change a lean mix, but only in the half throttle position (basically). lowering reduces fuel flow, so lean, raising increases fuel flow, so rich. the needle has a clip. look at it with clip up . raising the CLIP lowers the NEEDLE. and vice versa.

    main jet size is the major factor in running rich or lean and is the first part to "tweak". stock standard is usually RICH or too large.

    i smoke. not cigars :jester:

    but smoke is no way to test for an air leak, sorry. the aerostart method is mentioned. another one is to smear the manifold with grease, covering the joint between it and cylinder, and it and carb. if either method cures the idle issue, its an airleak. alcohol deodorants, (lynx for example) anything in a can that is highly flammable EXCEPT FOR BUTANE is the ideal testing stuff :) as long as it has a misty spray nozzle.

    also check cylinder base gasket, same method. grease or a can of propellant

    make sure the carb pushes ALL the way onto the manifold. push it on, scribemanifold at the end of carb spigot, remove carb...measure depth of carb spigot. measure how far up manifold your previously scribed mark is. they should be the same within 1 mm.

    sometimes it just needs a good push, sometimes you need to file away a bit of the weld on the manifold, or the spigot on the carb to let it go all the way on.

    spigot=clampy bit

    normally a small air leak on the intake will make idle too fast. but it isnt such an issue at wide open throttle. a leak on the cylinder base gasket will affect from idle to WOT.

    head gasket leak can, too.

    popping. could be anything without hearing it.. leaking head gaskets pop/squeak.

    pop magneto cover off and make sure that magnet key is in place and hasnt sheared/ is missing. could be that the ignition timings way off as magnet may have spun on shaft.
    Last edited: Oct 17, 2013
  8. CarbonBikes

    CarbonBikes New Member

    Well the black carburetor thing that's attached to the throttle cable was stuck (dunno how?) I got that fixed but there's black... stuff... looks like oil but doesn't smell like oil or gas is coming out of somewhere. I think I might've blown the head gasket but I don't know how. It looks perfectly fine. So that's why I don't think it's that. I've already checked the gasket below the head gasket (the one below the cylinder body) and that one's fine- (there's no black stuff near that one).

    So I guess I'll be ordering a new head gasket and seeing if that's the problem or not.
  9. CarbonBikes

    CarbonBikes New Member

    I don't know what that is but everything that's on my bike is stock besides the rear sprocket (which is a 32 instead of a 44). Oh and the chain is a 41 roller instead of the stock one. That fixes the chain breaking issue and the chain slipping off issue.

    Other than those two things the kit's stock
  10. crassius

    crassius Well-Known Member

    first thing to do with leaks is to clean everything really well, then run it just a little & look for first place oil shows up - no oil, run it a bit more & look again - repeat as needed
  11. HeadSmess

    HeadSmess Well-Known Member

    the black thing on cable...i can only think you mean slide?

    yes, they go in one way only. theres a slot on the side that cable tucks into. inside the carb, theres a small brass pin. opposite the idle screw.

    slot and pin engage, keeping slide straight. any other direction and theyll jam.

    the black stuff, the oily goop, it wont smell like oil or gas as its BURNT.

    look really close at the exhaust gasket, then forget it.

    pop cylinder head off. 4 nuts. any leakage past the head gasket is obvious with just a glance. a big brown black streak, or even a section missing... if its clean alloy all round, its fine. ditto head and cylinder faces. clean is good, streaks are leaks...

    could be you have a 66 with one of the slant heads that caused me to badmouth 66's? some warp. mine did :) once again, the marks are obvious upon dismantling.

    the only other leaks i forgot to mention!

    undo magneto cover. if theres any oily residue in here, the crank seals leaking.

    ditto on the clutch side. remove cover, check around small crank gear. leaks stand out like sore thumbs.
  12. CarbonBikes

    CarbonBikes New Member

    Well it seems to be coming out of either the exhaust port (which I don't see how that's possible- brand new cylinder body & exhaust gasket) or the place where the head meets the cylinder body. I guess it's a blown head gasket. Although the head gasket itself looks fine; no scratches, bumps, breaks, or nicks.
  13. crassius

    crassius Well-Known Member

    sometimes exhaust flanges are crooked and need filing to make a good seal - you do have a hanger on the muffler to keep it from shaking loose don't you
  14. HeadSmess

    HeadSmess Well-Known Member

    the exhaust always leaks. its a way to make sure the engines running, as the muffler is so effective :)

    remove the head. inspect gasket, any large scorched patches, or streaks where an OBVIOUS LEAK has occurred, means it HAS leaked. otherwise, replace head and do it up, tight. in a cross pattern on the studs, slowly and evenly, a bit at a time. then forget about black stuff, and start concentrating on if this bike is running correctly now or not.

    all the way back to the beginning again...is the plug tight?