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Old 03-19-2017, 04:52 PM
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Default 86 cr125 not starting after top end rebuild

     

Ok so I can't get my bike started after a fresh top end rebuild , the bike never started very well before it blew up but I just figured it had low compression. So it has great compression, gas , and spark now after the rebuild but it won't even pop or anything it just seems to not fire at all I also tried pop starting it and the piston just went for a ride. The piston is in correctly so could it possibly be spark timing being off ?
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Old 03-19-2017, 05:31 PM
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If compression is indeed good, and you have a strong blue spark and the bike is getting gas, ie plug is wet after you try and start. I would check the carb float is set right and carb is nice and clean inside. Then I would check the timing as it could be out and this would cause starting issues also.

Will
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Old 03-19-2017, 06:44 PM
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How do I check the timing ??? Because I put gas in the cylinder just to see if it was going to work but nothing so I'm going to guess it's timing
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Old 03-19-2017, 06:48 PM
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What color is the "spark"?
What is the compression reading?
Has the carb been cleaned?

Paw Paw
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Old 03-19-2017, 06:56 PM
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As pawpaw says check you have a quality spark and measuring compression. Just so you can eliminate two simple causes first. Timing is model specific, generally there is a woodruff key locking the position of the flywheel, and you adjust the stator position to change where spark happens. On a two-stroke the timing mark on the flywheel should be passing a mark when the piston is a certain measurement before tdc, as I say it is model specific and a shop manual is a must for any bike for this kind of information. Sorry if my explanation is a bit off, as I say the book is a must!

Will
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Old 03-20-2017, 07:02 AM
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Spark color is blueish and the compression is very good , I never touched the stator or flywheel when I rebuilt the top end so I don't understand the spark timing I guess
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Old 03-20-2017, 09:08 AM
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Quote:
Originally Posted by Jordy_3 View Post
Spark color is blueish and the compression is very good , I never touched the stator or flywheel when I rebuilt the top end so I don't understand the spark timing I guess
See if you can find some YouTube videos that demonstrate how to check/adjust timing.
Here is a great photo from dogger315 demonstrating how to set proper timing on a CR500, notice the alignment mark in the stator plate is lined up with the pointer molded into the cases (yellow arrow toward the bottom):



To change or adjust the ignition timing you'd have to loosen the two stator retaining bolts (red arrows) and turn the stator plate until it was where you wanted it to be.
I'm not familiar with the ignition on your bike at all, but notice the small black box on the upper right portion of the stator? That part (whose name fails me at the moment) is what actually generates the spark to the plug on a CR500 and many CR250's, so it may be similar on your bike. It can also be adjusted and needs to have the proper air gap between itself and the flywheel to generate the proper amount of spark. That's something else you may look into as well.
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Old 03-20-2017, 12:41 PM
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This doesn't make sense to me why the spark timing would be completely off if I never even touched the flywheel?
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Old 03-20-2017, 12:55 PM
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You say the bike has always been hard to start, 2 strokes vibrate alot, the bike is 31 years old. It's not crazy to think something may have shifted over the years. If your spark and compression is good and it's getting fuel you may as well check it.

Will
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Old 03-20-2017, 01:26 PM
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Quote:
Originally Posted by Jordy_3 View Post
This doesn't make sense to me why the spark timing would be completely off if I never even touched the flywheel?
It may have been off to begin with, and it's not hard to check. However, if you need to move the stator to correct timing you'll need a flywheel puller.
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Old 03-20-2017, 02:33 PM
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You should have a very bright Blue spark. Anything else is not good.
Clean carb and jets.
Ohms test the coil and stator.

Paw Paw
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Old 03-20-2017, 04:25 PM
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Ok so I ordered a puller so does anyone know if the timing markes will be the same as the photo above ?

---------- Post added at 06:25 PM ---------- Previous post was at 06:23 PM ----------

Also will I have to replace the woodruff key?
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Old 03-20-2017, 06:26 PM
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Should be similar as it's a Honda also. Try Google or YouTube model specific. Or like I say, splash out for a shop manual. Has all the info for your bike when you need to reference stuff like this. Best money you can spend on a bike if you work on it yourself.

Woodruff key should be fine. Only one way to find out. Pull off the flywheel.


Will
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