two stroke ignition timing - expert advice?

Discussion in 'The Garage' started by stainlesscycle, Aug 31, 2010.

  1. stainlesscycle

    stainlesscycle Long timer

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    ok, so i have a freshly rebuilt can-am 175. i have the squish on the loose side (1.2mm squish, spec is 1mm max) - i can run a thinner base gasket, which i have ordered, but the thinner base gasket will only get me to 1mm which is definitely on the safe side..

    stock ignition timing is 1.07mm btdc which felt a little pedestrian.. so i set ignition timing at 1.27mm btdc. i believe this is only a degree or 2. bike with this setting has nice over rev, and a nice hit. the question is this. since i have lower compression, the ignition advance should be fine or am i thinking all wrong? how far can i push this timing? it absolutely does not ping at 1.27mm, and runs excellent - i have b9es plugs (stock) - should i try a cooler plug just in case? i am running 93 octane always.... am i flirting with disaster?
    #1
  2. anotherguy

    anotherguy unsympathetic

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    Plug range will not cover too much timing. Continue with what works. What's the plug look like?Any pepper,that is little black spots on the insulator? A definite sign of detonation. Do a full throttle (fourth/fifth gear) plug reading on a new plug with a fully warmed engine and look for pepper or little silver spots. The silver spots are extreme detonation damage,small pieces of piston. You can push the timing to the point of detonation and then back it off but if you melt a piston doing it it's not my fault. :cry

    P.S You live close enough I could help ya. If ya really wanna take a ride I'll be in Gaithersburg MD Saturday the 4th doing some dyno work and we can sort it with printouts! :evil

    Edit: Do you know how to read plugs for timing? Look at this photo. See the center electrode? At the tip of it there's a clean area about 1MM wide. That's correct timing. Less is too little advance,more is too much. Oh and the mixture is good on that plug as well.

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    #2
  3. stainlesscycle

    stainlesscycle Long timer

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    i thought you read timing on side electrode.....i look for line on strap, it should be about halfway right? pics coming of 3rd gear uphill WOT plug chop..
    #3
  4. stainlesscycle

    stainlesscycle Long timer

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    this is a fresh motor, under 1 hour run time. oil injector is still a bit enthusiastic at wot. and still dinking with jetting. it's a fricking bing, so i got no jets, waiting for them to show up.

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  5. stainlesscycle

    stainlesscycle Long timer

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    and here's plug after oil cleaned off.


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    #5
  6. anotherguy

    anotherguy unsympathetic

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    The reason it's running better with more timing may be making more real time available to burn off extra fuel. Get the jetting closer before messing with the timing any more. The plug isn't getting hot enough with the extra fuel to give an accurate reading. Combustion temps are very low when rich and everything else is affected.

    Never used the side electrode for anything other than determining heat range.
    #6
  7. stainlesscycle

    stainlesscycle Long timer

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    cleaned up jetting a bit. still need to go one leaner on the main (gotta wait for it to show up..), and then reset needle.. (i'm at #1 on needle...)


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    #7
  8. anotherguy

    anotherguy unsympathetic

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    Progress. See how the electrode is beginning to clean up as combustion temps increase?

    I know this is about timing but get the pilot circuit sorted before moving up the scale. Carb circuits are additive so the lower ones add to the upper ones. Just makes it easier so you only have to do it once. Do you have the Sudco catalog? It covers it pretty well.

    BTW nice photos.
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  9. stainlesscycle

    stainlesscycle Long timer

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    pilot/air screw is done. i get that first. the main is just plain old too big. with the right main, i can move the needle back up and get a better transition. then reset air screw and get accurate readings.. i'm 2 turns on the air screw, and i feels fine to 1/4 throttle - it actually feels fine through the whole throttle range - no lean spots, no bog or hesitation, nice instant response. but i know it can be better. it still starts very easy even with timing advanced. i know .2mm is not drastic... i know it's impossible to do jetting when i'm gonna change the squish, and screwing with the timing at the same time. i just wanna ballpark it, and have an idea of where to go when it's all installed..i needed some jets for this thing anyways..
    #9
  10. fritzcoinc

    fritzcoinc Enjoying my last V8

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    How did you get the killer photos of your plugs?
    By the way, I also use the strap to read plugs. Black/carbon just above the weld is pretty close.
    #10
  11. Middleweightboxer

    Middleweightboxer Middleweightboxer

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    Looking at the first picture, you should be observing the color of the ring at the base of the insulator or in the case of this cutoff plug at the waist. The brown ring is what you are looking for. If it were rich the ring would be blacker and lean/ighter colors as you move away from the brown.

    Plug reps use a lighted pocket scope to magnify and observe the color of the ring.
    #11
  12. stainlesscycle

    stainlesscycle Long timer

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    sony dsc-h2
    macro setting
    with flash and i didn't zoom in (if you try to get to close, the flash has no affect) - i cropped a 3mp image with irfanview

    http://www.dpreview.com/reviews/sonyh2/

    i love the camera - the only digitial i've ever owned that has accurate color rendition for relatively cheap (i paid less than 200 for it several years ago.) it takes close to 1000 3mp images on a set of rechargeable batteries. takes a beating too, mine is covered with grease.
    #12
  13. stainlesscycle

    stainlesscycle Long timer

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    yes, i'm aware of that, but i'm still so rich, it's hard to read anything. waiting for main jets....
    the pics were an attempt at getting a good shot of the electrode
    #13