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Old 01-09-2014, 06:35 PM   #1
piniongear OP
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Question regarding setting the timing on 1976 YZ175

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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Old 01-09-2014, 06:59 PM   #2
joexr
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It's supposed to be advanced. Why are you screwing with it in the first place?
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Old 01-10-2014, 07:23 AM   #3
piniongear OP
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Originally Posted by joexr View Post
It's supposed to be advanced. Why are you screwing with it in the first place?

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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Old 01-10-2014, 07:54 AM   #4
joexr
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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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Old 01-10-2014, 08:57 AM   #5
anotherguy
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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.
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Old 01-10-2014, 10:01 AM   #6
piniongear OP
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Originally Posted by joexr View Post
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.
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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Old 01-10-2014, 10:44 AM   #7
baloneyskin daddy
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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.

baloneyskin daddy screwed with this post 01-10-2014 at 10:55 AM
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Old 01-10-2014, 10:56 AM   #8
baloneyskin daddy
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I think I'm full of shit on that last response
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Old 01-10-2014, 12:25 PM   #9
Tim McKittrick
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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!
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Old 01-10-2014, 03:48 PM   #10
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OK. Just trying to help.

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Old 01-10-2014, 04:04 PM   #11
piniongear OP
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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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Old 01-10-2014, 06:35 PM   #12
anotherguy
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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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Old 01-10-2014, 07:08 PM   #13
piniongear OP
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Replacing the crank seals would be prudent. At the very least a pressure and vacuum test for verification.
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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Old 01-11-2014, 01:47 AM   #14
stainlesscycle
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Quote:
Originally Posted by joexr View Post
. The longer center mark should be piston top dead center.
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..
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stainlesscycle screwed with this post 01-11-2014 at 02:00 AM
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Old 01-11-2014, 06:00 AM   #15
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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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