Question regarding setting the timing on 1976 YZ175

Discussion in '2 smokers' started by piniongear, Jan 9, 2014.

  1. piniongear

    piniongear Adventurer

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    I am rebuilding my 1976 YZ175C and have come to the point where I need to set the ignition timing.
    I find there are three slash marks on the stator, and a single mark on the crank piece.
    The center mark is longer than the marks to the left and right of center on the stator.

    When I pulled the engine down I found the engine timing was set with the stator being rotated fully clockwise to the end of the slots. The timing mark on the crank piece was well in front of the 3 marks on the stator.

    I bought this bike new in 1976 and I am the only owner.
    This is the first time the engine cover has ever been removed, so that is the way the timing was set at the factory.
    I find it hard to believe the factory set it that way, but it is how the engine timing was set at the factory. The bike always ran well.

    So now comes my question:
    Having set the engine at .083 BTDC the mark on the crank piece lines up perfectly with the longer center mark ........ IF the stator is rotated fully counter clockwise to the end of the slots.

    Can someone explain what the 3 marks mean and where do I align the mark on the crank piece to achieve correct timing?
    I see no reference to the 3 marks in the manual.

    Thanks to anyone who cares to post a comment.
    pg
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  2. joexr

    joexr Banned

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    It's supposed to be advanced. Why are you screwing with it in the first place?
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  3. piniongear

    piniongear Adventurer

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    I would hardly calling it 'screwing with it'.
    All I want to do is set the ignition timing correctly.
    The factory had the timing stator plate rotated fully CCW and the correct setting seems to be fully CW rotation of the stator plate.
    Both positions seem suspect to me.

    I am just asking for advice from someone who has knowledge of how to set the timing.
    I am only trying to follow what the book says under 'ignition timing'.
    pg
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  4. joexr

    joexr Banned

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    I apologize , I misunderstood what you originally said. It was retarded since you got it. Yes it should be advanced , firing before top dead center. The longer center mark should be piston top dead center.
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  5. anotherguy

    anotherguy unsympathetic

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    Do you know how to read timing on a spark plug? I ask because setting the timing via 1976 instructions may lead to detonation because of unleaded ethanol diluted fuel. Fuel was much better in 1976 than now.

    See here.
    #5
  6. piniongear

    piniongear Adventurer

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    No problem joexr.....
    Yes, from the factory the timing was retarded to the max, since the plate was rotated to the end of the slot.

    Now I find that lining up the center mark on the stator leaves the plate at the opposite end of the slot.
    It seems to me that they would have had the approximate timing with the hold down screws in the middle of these slots.

    Anotherguy...... I understand what you're saying about the gas being different today, but I run all of my other vintage bikes with the timing set by the book with no problems.
    So other than having to line my fiberglass fuel tanks, I see no reason to do anything different just because today's fuel is a 10% ethanol mix.
    pg
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  7. baloneyskin daddy

    baloneyskin daddy bikaholic

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    If the motor spins CCW and you turn the plate CW that's advancing the timing as it fires sooner in the stroke. I think it was correct.
    #7
  8. baloneyskin daddy

    baloneyskin daddy bikaholic

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    I think I'm full of shit on that last response :lol3
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  9. Tim McKittrick

    Tim McKittrick Long timer

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    I only have experience with the DT175's of this vintage..... On those motors the marks on the plate didn't seem to have a great deal of correlation to the actual timing point. Also, a worn lift shoe on the points will alter everything as it changes the opening time of the points. On the DT one has to set the point gap to the desired opening before mucking with the timing. Once that's set you can then get the dial indicator out and set the point opening point to however many mm before TDC is required.

    And I only mention this because I've done it- make sure you are turning the crank in the correct direction and you are setting the timing to BTDC and not ATDC. The DT actually ran when set wrong.... Just not very well!
    #9
  10. anotherguy

    anotherguy unsympathetic

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    OK. Just trying to help.

    [​IMG]
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  11. piniongear

    piniongear Adventurer

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    Well guys, thanks for your comments and suggestions.
    But the YZ175C has electronic ignition (no points) and I have the piston sitting at exactly 2.1mm (.083) before top dead center.
    Lining up the marks results in the stator plate being rotated fully clockwise (advancing the spark a long way from where I saw it was set at the factory)

    I guess all I can do is set it using the timing marks or set it back to where it was, as the engine ran fine for a year at that setting.
    After that year (1976-1977) the bike was parked and never started again. So after almost 37 years I am now working on restoring the bike.
    Thanks again for your comments.
    pg
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  12. anotherguy

    anotherguy unsympathetic

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    Replacing the crank seals would be prudent. At the very least a pressure and vacuum test for verification.
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  13. piniongear

    piniongear Adventurer

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    Good point! Thanks for the reminder.
    I recently replaced the crank seals on my 1973 Bultaco Astro and my 1975 Bultaco Pursang.
    They were leaking badly and I really had trouble getting the Astro 360 engine to seal, but was finally somewhat successful.
    I have ridden it in three races since then and it is running fine.
    I WILL replace the seals in the YZ175.
    pg
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  14. stainlesscycle

    stainlesscycle Long timer

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    i don't know about that. the longer center mark is proper timing (say 2.00mm or so) and the other 2 are the most advanced and most retarded that is recommended.... i don't think there will be a tdc mark. the only internal rotor yamahas i have from that era are mx250 and yz125x/c - and that's how they are..

    i have a bunch of early mx175 (electronic ignition) and the timing/cdi are similar (although external rotor). i set them around 1.6mm - but i use a different cdi and source coil - anywhere between 1.2 and 2.4 should be safe - run it and see how it performs.. the yz175,mx175, it175, it125, dt125,dt175,rt180 are all similar stroke/port timing, therefore the ignition timing is about the same..
    #14
  15. anotherguy

    anotherguy unsympathetic

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    The hole in the above piston was made at 2.0MM BTDC. Tread carefully.

    The difference between ethanol fuel and old gasoline is the water absorbed by the alcohol. It becomes emulsified and reduces the weight (air:fuel is weight,not volume) of the combustible charge leading to a inconsistent mixture. 4 strokes have enough latitude to shrug it off. Old racing 2 strokes do not. Run race fuel appropriate to compression for best consistent results. Not to mention 2 strokes just love leaded fuel.
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  16. piniongear

    piniongear Adventurer

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    Thanks for your reply stainless.
    I am not looking for there to be a TDC mark (I can find that with a dial indicator) but I agree with you that the two smaller marks are to indicate maximum advance and retard positions.

    What puzzles me is from the factory the setting was nowhere close to these 3 timing marks and the engine ran perfectly.
    Now I am trying to set this ignition timing and to get the rotor mark to line up with the center timing mark leaves the stator rotated fully clockwise.
    Just the extreme opposite direction of where the factory set it.
    What bothers me is I do not believe either setting could be right because I would not expect to find the adjustments to be tight against the end of the slot(s).


    I was also surprised to find this engine has no flywheel, just a small rotor.
    Is an engine flywheel not used, and if so....Why is that?
    Just trying to learn something about this engine.
    pg
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  17. stainlesscycle

    stainlesscycle Long timer

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    it is possible the flywheel key is missing and that's why the marks are not lining up. but since you are the original owner i doubt it - unless it has sheared and slipped a bit....you'll find out when you replace the seal....

    inner rotor ignition are snappier..lots of yz yamaha's had inner rotor...

    the timing is pretty forgiving on these motors - i've been all over the place on them - between 1mm and 3mm it'll run fine. i can't really recommend timing it much more than 2.5mm though... what was the timing with the 'factory' setting as it was when you opened it up?
    #17
  18. piniongear

    piniongear Adventurer

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    Ah! I must admit to being a 4 stroke guy and this (and my Bultacos) are the first 2 strokes I have ever worked on.
    So what you say regarding the fuel makes good sense and I do see the hole in your piston!
    Thanks for the comment.
    pg
    #18
  19. piniongear

    piniongear Adventurer

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    You read my mind there.
    I am going to set it where the factory setting was and see what the timing is BTDC. It was really retarded, but I do not know how much.
    As soon as I can measure it I will get back.
    I also will look at the rotor and key but would be surprised to find it had moved. This engine is just as it came from the factory and is even as clean inside as a new engine because it was ridden so little.
    I bought the Yammie and within a year later bought a Bultaco Pursang 250.
    I stopped riding the YZ because I liked the low end torque of the 250 Bul better. So it was ridden very little that first year and then went into storage.
    pg
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  20. stainlesscycle

    stainlesscycle Long timer

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    i did fail to mention i'm running a mix of 112/93 fuel, so that lets me push it a bit more than pump gas..... and i have compression bumped up a bit..... with a stock yz175 head, the compression is not obnoxious, it has a pretty big squish.....
    #20