Help judging Spark plug

Discussion in 'Motorized Bicycle Trouble Shooting' started by Miguel P, Sep 10, 2017.

  1. Miguel P

    Miguel P New Member

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    Hi
    Any 2stroke wizards could help me judge this spark plug?

    It has been driven whole throttle range. It is a NGK B6HS on 50cc HT engine with needle on second position from top and standard jet (unknown size).
    It has been around 20-25 Celsius lately and I'm using 24:1 synthetic oil and 95 octane no ethanol IMG_20170910_175949.jpg IMG_20170910_175923.jpg IMG_20170910_175856.jpg IMG_20170910_175853.jpg
     
  2. crassius

    crassius Well-Known Member

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    doesn't look horrible - perhaps a bit on the lean side or plug is one number too hot
     
  3. allen standley

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    I agree crassius, looks slightly lean, If it were me I'ld go 32:1 tho. That's just me.
     
  4. Miguel P

    Miguel P New Member

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    I don't know how hot it gets but by quickly touching the cylinder it doesn't seem hotter than when it was with 16:1 and overly rich..

    It has been pretty warm and dry around here and being slightly lean.. I'm a little reluctant to lower oil concentration much more until I enrich the mixture, which was my second question seeing that you also think it's lean: Given that even at WOT it is lean, as that plug is the result of whole throttle range and that that can only be changed by a larger jet, should that be my next move? Larger jet then perhaps readjust the needle given the new jet, change to 32:1 and recheck plug/new plug?

    Alternatively I was going to try this foam material that I have (lots) because the stock air filter material seems too permissive. I guess that would enrich the mixture right? but that would just be choking the engine.. Wouldn't you say that it would likely lead to a bigger loss in power than the richer mixture by a larger jet would? (assuming I am at peak power at slightly lean as it is)? Also in terms of power and lifetime, how would those two cenarios compare to just using the colder NGK B7HS that I also got when the guy asked: B6?? "What the **** is that for?!"
    I mean, for context, I'm pretty content with the way it handles, I can cruise at ~40km/h at 2/3 throttle flat road and I have reached almost 60 with engine screaming and rear wind. In terms of power I'm OK I'm just a little worried with the lifetime.

    What do you reckon?

    Thank you both for your time
     
  5. crassius

    crassius Well-Known Member

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    I like changing things that can easily be changed back, I'd start by just raising float level a tad and see what happens.
     
  6. Tony01

    Tony01 Member

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  7. Miguel P

    Miguel P New Member

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    Hi all

    I had some time to test after your tips
    I started by just swapping for a colder plug b7hs and it turned out pretty much the same before. And I should say looking at it again the 2nd photo I posted is closer to reality, white/grey that is. For some reason the last photos, which were taken in the sun, are chocolaty which is not true,sadly.

    Second thing I tried, after putting the b6hs back on, was to check the float like Crassius suggested. I read that stock distance is 21mm.. It was more like 15mm from factory. Just for the sake of it, I set it at 21mm and it ran pretty much the same except at both WOT and high RPM/speed, above 40km/h where it would die down, like if I had hit the kill switch.. So I set it back to 15mm float level which was actually as much as it would go up..

    Lastly I wanted to eliminate the chance of any air leak so I put a bunch of silicone glue around the intake manifold where the NT carb is sitting and tightened it on as much as I could and plug still looks white/grey..

    This was all with needle on 2nd notch from the top.. so I am aware that is easily tuned to enrich but my idea has been from the start to get the WOT tuned first to avoid the rest of the throttle range to confound it, like as the engine warms up before testing, as I get up to speed etc..
    So anyways I have gotten new jets 0.01 mm of increments from .60 to .80 so 21 different sizes and was thinking of starting with 0.75mm and a new fuel filter and clean air filter(stock) just in case.

    What do you guys reckon? Also and maybe most importantly am I right to assume that a plug condition/color is cumulative from lean to rich as in a white/grey plug CAN get darker/brown but NOT the other way around?

    Thanks
     
  8. crassius

    crassius Well-Known Member

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    color should advance along the center porcelain of the plug - just a bit of white around electrode and getting darker as one looks up into plug
     

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