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Old 01-11-2014, 06:07 AM   #16
piniongear OP
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Joined: Dec 2013
Location: Texas
Oddometer: 10
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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Old 01-11-2014, 06:16 AM   #17
stainlesscycle
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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?
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Old 01-11-2014, 06:23 AM   #18
piniongear OP
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Quote:
Originally Posted by anotherguy View Post
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.

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
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Old 01-11-2014, 06:31 AM   #19
piniongear OP
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Quote:
Originally Posted by stainlesscycle View Post
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?

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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Old 01-11-2014, 07:28 AM   #20
stainlesscycle
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Quote:
Originally Posted by stainlesscycle View Post
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...
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.....
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