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YZ 250 CDI on YZ250X

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I'm hoping someone can help me out here.  So I tried my buddies CDI from his 2006 YZ250 on my 2017 YZ250X and really liked it, and I'd like to pick one up used. 

I know that 2006 to 2019 CDI will work, but I found one from a 2002 YZ250 locally for a good deal.  Am I safe to run this CDI? And, will if work?  From the reasearch I've done I see that people use CDI's from newer bikes on 2002-2005 models, but I haven't heard of going the other way.   

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The CDI's are basically the same, with the X being retarded 2 degree from the YZ. Just increase your timing +1 degree and you'll be very impressed.

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49 minutes ago, Doc_speeder said:

Not sure, but what did you like about it?  How did it feel different than stock?

Well its hard to describe exactly.  For example, when I was on say a tricky climb at low speeds's the bike just seemed to run poorly and sluggish.  When using the CDI from the non-X bike it ran far better and the power seemed more predictable and responsive.  I never had a problem in faster or higher rpm situations, its mostly in technical situations.

We put the my 250X CDI on my buddies YZ and the problem then appeared on his bike.  

For the longest time I thought it was jetting and I kept chasing that, but this seemed to help out quite a bit.    

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27 minutes ago, 218 said:

The CDI's are basically the same, with the X being retarded 2 degree from the YZ. Just increase your timing +1 degree and you'll be very impressed.

Ok, thats good to know.  I do have a RK Tek head on the bike so it does have higher compression.  But if the main difference in CDI's is changed timing, there shouldn't be anything to worry about increasing the timing one degree? Since it seemed ok with the non-X CDI

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Well you already answered that question by running the YZ CDI box without any problem. So, yes, there are no worries about increasing the timing just one degree even with a YZ type head and compression ratio. You can increase the timing two degrees and achieve the same effects as installing the YZ box, but if you like the X bottom end power at all, then just try one degree first. I think you'll be impressed.

The disclaimer here is that you haven't leaned the crap out of your X jetting. By increasing your compression to standard YZ spec's and increasing the timing as well, you will basically have a YZ engine with an X power valve mod.

Edited by 218
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2 hours ago, 218 said:

Well you already answered that question by running the YZ CDI box without any problem. So, yes, there are no worries about increasing the timing just one degree even with a YZ type head and compression ratio. You can increase the timing two degrees and achieve the same effects as installing the YZ box, but if you like the X bottom end power at all, then just try one degree first. I think you'll be impressed.

The disclaimer here is that you haven't leaned the crap out of your X jetting. By increasing your compression to standard YZ spec's and increasing the timing as well, you will basically have YZ engine with an X power valve mod.

 

I enriched the jetting a little when I installed the head, so I think I should be good.  I'll try advancing the timing one degree. 

Thanks very much for the info, it's very helpful.

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Good deal. A lot of guys seem to be leaning out the X's quite a bit because of the excessive squish clearance. Just wanted to make sure that wasn't your case. But, as you stated you already have the more YZ like head and richened your jetting, so you are probably good. You seem to already know, but it's just mainly the 1/2 throttle up jetting you need to worry about when doing this. Good luck.

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On 8/29/2019 at 7:08 AM, 218 said:

The CDI's are basically the same, with the X being retarded 2 degree from the YZ. Just increase your timing +1 degree and you'll be very impressed.

Source on X ignition simply being retarded 2 degrees from standard YZ? Good info!

Edited by SoCalMX70

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On 8/29/2019 at 12:10 PM, 218 said:

Good deal. A lot of guys seem to be leaning out the X's quite a bit because of the excessive squish clearance. Just wanted to make sure that wasn't your case. But, as you stated you already have the more YZ like head and richened your jetting, so you are probably good. You seem to already know, but it's just mainly the 1/2 throttle up jetting you need to worry about when doing this. Good luck.

I advanced the timing 1 degree and rode it last weekend.  It was running significantly better.  Still not exactly where I want it to be, but this has made a huge improvement and I feel like I'm on the right track!

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Then go ahead and try 2 degrees. Most are usually happy with 1, but it seems you want a YZ powerband.

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