2-stroke timing

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#1
125sx engine timing
Inadvertantly my timing has been moved thanks a little twerp at the track trying to do me a favor. :ugg:

It feels and sounds to be running a little flat on top and looking at my plug I may be encountering some detonation. I see in the book that timing should be set to 16.5 btdc but how exactly is this measurement accomplished? It can't be as simple as connceting a timing light I'm sure but other than just playing with it I have no idea how to reach the specified adjustment.
 
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#2
Originally posted by Jeff Gilbert
I see in the book that timing should be set to 16.5 btdc but how exactly is this measurement accomplished?
Jeff.

It depends on if it is 16.5 mm or 16.5 degrees btdc. If it is 16.5 mm, then you have to use a dial indicator that screws into the sparkplug hole and measures 16.5 mm of piston movement before top dead center.

If it calls out for 16.5 degrees. Then you have to use a degree wheel that fits on the crankshaft and measures how many degrees of movement of the crankshaft before top dead center.


Just my $ .02 :thumb:
 
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#3
yep, or just pop off the cover on a stock like bike, and copy it...tho normally the original setting left some kind of marks on your plate, did it not?
 
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#4
Timing is 1.4mm (0.055 in) btdc or 16.5 degrees btdc.
Yes there are 2 marks on it and they about .5mm apart or closer.
 
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#5
Originally posted by Jeff Gilbert
Timing is 1.4mm (0.055 in) btdc or 16.5 degrees btdc.
Yes there are 2 marks on it and they about .5mm apart or closer.
Jeff.

That sounds more like it.

If you can find a dial indicator you could set the timing and then mark the plate. If you have two marks on the plate, the first mark should be the timing mark and the second one will be tdc. You could take a small screwdriver and through the spark plug hole check for tdc. If at tdc the second mark lines up, then your first mark should be the timing mark.

To be sure, I would check it with a dial indicator.
 
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#6
Didn't get a chance to try the dial indicator but I lined up to the 2nd mark & it runs like a scawlded ape again. I tried moving it to the other mark the last time, after I realized what had happened and I guess I didn't have it quite right because it sure didn't run like it does now. Very touchy thing isn't it?
 
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#7
You can check your adjustments with a timing light, just need a 12V supply for the light. When using the dial indicator and degree wheel, make sure to find "true" TDC. There is dwell time, time that dial indicator will not move but crankshaft is, before and after TDC.