1981 YZ125 4 Stroking at Idle

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10/10/2018 6:08 PM
Edited Date/Time: 10/10/2018 6:10 PM

Ok, so I recently replaced my stator with a new one from Ricky Stator, following a complete stator melt down. When I start my YZ it is firing on every other stroke, at idle. I’ve read that they call this 4 stroking. Anyway, I replaced the CDI with another unit from a running bike and it’s doing the same thing. The spark plug has lots of blue spark. I even replaced the plug with the same results. The ignition coil has ohm readings that check out OK, so I am at a loss as to what to do next. As a side note, I had honed the cylinder, put in new piston and rings and replaced all seals in the engine, and rode it, prior to the stator melt down. I believe the stator melted down, as the flywheel wasn’t seated correctly over the woodruff key, so the flywheel spun on an eccentric, touching the stator coils and subsequently sorting them out. I have since replaced the flywheel and assembled it all correctly.

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10/10/2018 6:09 PM

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10/10/2018 7:39 PM

When a bike is overly rich it will 4 stroke. Do you have the stock pilot installed? Then again, most jetting problems are electrical.

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10/10/2018 8:00 PM

Yes, stock jets. It was running fine before, but I replaced the stator and flywheel, so I’m beginning to think I need to retard the timing a bit.

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10/11/2018 6:28 AM

Check it with a dial indicator. I made my own holder by cutting the insulator out of a spark plug and threading a set screw in it to hold the gauge in the cylinder. I'll have to see if I can find the old link with the DIY.

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10/11/2018 6:32 AM

I own a dial indicator for setting timing. I am going to check it and make sure it’s correct. If it is, I’m going to try retarding it a bit more and see if that helps.

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10/11/2018 6:34 AM

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10/11/2018 6:36 AM

Yeah, this is a motion pro gauge, but I’ll bet it was made in China.

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10/11/2018 10:12 AM

Talked to the Ricky Stator people. Turns out I have the stator coils in upside down. That is why it’s 4 stroking.

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10/11/2018 10:40 AM

Glad that you got it squared away!

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10/11/2018 5:55 PM

Got it running again!!! Photo

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