What's your hunch on this combustion noise?

Discussion in '2 smokers' started by frascati, Jun 30, 2019.

  1. frascati

    frascati Adventurer

    Joined:
    Mar 23, 2018
    Oddometer:
    57
    Location:
    michigan
    Just off the top of your head.
    My little puch e50 has a problem with high rpm "rattling" "buzzing" hard to describe really.
    It's happening right at the combustion chamber (easy to locate noises on this little exposed engine).
    It could be electric, fuel, compression, vacuum leakage, etc etc. I could describe the bike to a T but it might not help. I wonder if anyone with small two stroke experience might chime in with "check your...).
    Fine idle. Fine midrange. Fine, in fact, in most circumstances. When going uphill, or against the wind, at high rpm the engine starts hesitating and each hesitation is accompanied by this sudden onset of buzzing or high frequency rattling from the head.

    I can add more info if needed if anyones interested in guessing.
    #1
  2. frascati

    frascati Adventurer

    Joined:
    Mar 23, 2018
    Oddometer:
    57
    Location:
    michigan
    adjusted points. checked spark. new plug. float adjust. gone through a range of jets.
    Feels like it's not getting sufficient fuel. The "buzzing" that accompanys the power lag lasts for a few secs then surge, afew secs more then surge, on and on. Not a huge lag, but subtle and sporatic. but the buzzing sound that comes with it coming from the head seems like it might be a good clue to someone with tuning experience on these. I've even replaced the head with a spare. No change. and it hasn't always done this with the present set up. Just started a few thousand miles ago.
    #2
  3. snarlyjohn

    snarlyjohn Human money repellant

    Joined:
    Apr 1, 2016
    Oddometer:
    503
    Location:
    Australia
    I've experienced something similar with fuel foaming in the float bowl. Under normal conditions everything was fine but at high rpms and load the engine would falter for a second or so, just long enough for the rpms to drop out of the vibration zone, then it would pick up again and the cycle would repeat. The effect was a bit like a rev limiter. Of course this might have nothing at all to do with your problem but maybe it'd pay to check for loose engine mounts or anything else that might cause vibration at high rpms and loads. And of course it's very difficult to accurately locate the source of sounds - the true source often turns out to be somewhere totally different to where it appears to be from. I'd also be inclined to check fuel flow into the bowl and maybe have a close look at the piston for any signs of det or preignition or unusually high temps.
    #3