Converting the YZ250 motor into a 250X motor?

[Snider]

 I am interested in the CDI difference but it seems that experiment is around $200... Hopefully someone with both bikes can plug one in to each bike..YZ into YZX and visa versa... this would be of interest not only to YZ riders but YZX riders as well....

Edited February 16, 2016 by Snider

[rjpjnk]

 I am interested in the CDI difference but it seems that experiment is around $200... Hopefully someone with both bikes can plug one in to each bike..YZ into YZX and visa versa... this would be of interest not only to YZ riders but YZX riders as well....

 

I agree!

 

Interestingly, I bet it would cost almost nothing additional for Yamaha to sell a single CDI with both timing profiles built it and a simple switch or jumper wire to choose which one you want active. *That* would be cool!

[Rosehill Ryder]

 I am interested in the CDI difference but it seems that experiment is around $200... Hopefully someone with both bikes can plug one in to each bike..YZ into YZX and visa versa... this would be of interest not only to YZ riders but YZX riders as well....

I have both and have switched them . Its just a little more smoother and linear .Just a piece of the Pie of the X-puzzle . Bang for the buck , Change the PV-spring 1st and adjust the washers to your preference . Then the X Head  , then the CDI . I have just put another fresh (replated ) cylinder on . I went back stock . The additional $ 400 dollars for a new PV and X cylinder over just a re-plating , just was not that enticing at this time . Don't get me wrong if the cylinder had to be fully replaced I would have went that route . Again IMO (1) PV spring/washers (2) Head (3) CDI (4) PV and Cylinder . These are considered as bang for the buck . And no one may agree with me .

[Snider]

My nephew got hold of me last night.. sent a pic of him and his brand new 250X Next time he goes riding with me, I'll hit him up. Ha ha

[southutdez]

THANK YOU Rosehill! That was the type of answer I was looking for.

[rjpjnk]

I have both and have switched them . Its just a little more smoother and linear .Just a piece of the Pie of the X-puzzle . Bang for the buck , Change the PV-spring 1st and adjust the washers to your preference . Then the X Head  , then the CDI . I have just put another fresh (replated ) cylinder on . I went back stock . The additional $ 400 dollars for a new PV and X cylinder over just a re-plating , just was not that enticing at this time . Don't get me wrong if the cylinder had to be fully replaced I would have went that route . Again IMO (1) PV spring/washers (2) Head (3) CDI (4) PV and Cylinder . These are considered as bang for the buck . And no one may agree with me .

 

Thanks. Good info!

 

Regarding the cylinder, what do you mean you "went back stock"? Was the cylinder you were running stock or modified? That is, were you moving from a modified 250 cylinder back to a stock 250 cylinder or just replating your stock 250 cylinder? I forget what you are running.

[218]

I have both and have switched them . Its just a little more smoother and linear .Just a piece of the Pie of the X-puzzle . Bang for the buck , Change the PV-spring 1st and adjust the washers to your preference . Then the X Head  , then the CDI . I have just put another fresh (replated ) cylinder on . I went back stock . The additional $ 400 dollars for a new PV and X cylinder over just a re-plating , just was not that enticing at this time . Don't get me wrong if the cylinder had to be fully replaced I would have went that route . Again IMO (1) PV spring/washers (2) Head (3) CDI (4) PV and Cylinder . These are considered as bang for the buck . And no one may agree with me .

I agree.

 

I didn't go with a cylinder and power valve either. I opted to just port the stock cylinder for more mid to top. Then cut the stock head to 23.2cc and .040" squish. Added the CDI and PV set up, then I just installed '99 clutch springs.

Edited February 17, 2016 by 218

[rjpjnk]

I agree.

 

I didn't go with a cylinder and power valve either. I opted to just port the stock cylinder for more mid to top. Then cut the stock head to 23.2cc and .040" squish. Added the CDI and PV set up, then I just installed '99 clutch springs.

 

Did you compare the two CDI's to see what the X version brings to the mix? What spring and washer setup did you go with on the governor?

 

Good idea going with .040 squish and lowered compression. Must have had to take a lot of material out of that dome. Do you have any pics of the head?

 

Overall, what are your impressions of the ride now?

[rjpjnk]

... IMO (1) PV spring/washers (2) Head (3) CDI (4) PV and Cylinder . These are considered as bang for the buck . And no one may agree with me .

 

I agree too that this list is in the right order in terms of best bang for the buck. Of course, so far no one has actually replaced the cylinder or power valve, so I'm kind of guessing here.

 

If/when I do order the cylinder and PV the first thing I will do is compare the design to try to determine what Yamaha changed. Maybe the cylinder and PV are a waste of money. I might like my EG mo-betta better. Well, such is the price of science ? If I don't like it I'll ebay it. Maybe someone else wants to give it a try. Maybe I'll ebay the whole "250X conversion kit" as a set. At any rate, it should be good for one fun Summer!

[bobsled]

I think I like the gears as they are, but I did already move to the X clutch springs. I like the easier pull.

Just a heads up guys if you hard on the clutch don't do the X springs in the clutch you"ll only wear the clutch out faster.

So, we know the springs are different....are the clutches different?

I'm too lazy to look up part numbers or specs.

[mikenash]

So, we know the springs are different....are the clutches different?

I'm too lazy to look up part numbers or specs.

Same Clutch and parts just lighter springs for easier pull.

[bobsled]

Same Clutch and parts just lighter springs for easier pull.

Then I guess the additional wear is negligible? If it's good enough for Yam to call it good enough, I guess it's good enough.

[rjpjnk]

That's what I figure. I like the lighter feel.

[Rosehill Ryder]

Thanks. Good info!

 

Regarding the cylinder, what do you mean you "went back stock"? Was the cylinder you were running stock or modified? That is, were you moving from a modified 250 cylinder back to a stock 250 cylinder or just replating your stock 250 cylinder? I forget what you are running.

It was a stock cylinder from My 2003 model that was replated . And 2011 was stock also . It had 400 plus hours on it and plating was worn in a several spots .

[SDT YZ ESR 325]

ESR 325 - Is a BETTER solution!!

 

http://www.eddie-san...egory_s/126.htm

One Bike with the Broadest Linear Power Band - Awesome Value / Most Fun Motocross/Off-Road Bike!
There is no Replacement for Displacement!!! Repeat those words over and over because once you feel a 325 Two-Stroke Torque (close to a 450) down low, you will kick yourself for waiting to buy the kit!
Eddie Sanders Racing (ESR) http://www.eddie-san...egory_s/126.htm
Options:
325 (option-5 Oversize Pistons) (33% Displacement increase over 250) / 345 (option-2 Oversize Pistons) (38% Displacement increase over 250), Aluminum Cylinder (Can be Re-sleeved), Machined Head, Piston, Adjustable Power Valve and Gaskets a $900 to $1000 investment.
Options: Thinking of buying a 2016 YZ250X ($7,390), YZ250FX ($7,890), YZ450FX ($8,890) Model, if you have the money good for you. Or spend the money on a used Yamaha YZ 250 ($3K to $5K), add a skid plate, front disc cover maybe some other preferred items. After riding the YZ ESR 325 I would say, all the 250’s or 450’s are now second rate compared to the YZ ESR 325! I believe ESR is the best VALUE Big Bore with the BROADEST power band!
Yamaha YZ with ESR 325 Kit - (250 was 212 LBS. Dry - 228 Wet) (YZ 325 - 214 LBS. Dry est.)
Weight Benefit over YZ 250FX, (231 LBS Dry est. – 247 Wet or 16 LBS. heavier) YZ450FX (240 LBS. Dry est. – 262 LBS. Wet) – (30 LBS. heavier) (Note: Fuel weighs 8 LBS. / 1 gal.)
Recent Rides: YZ ESR 325
-MX Tracks, torque out of the turn, nice linear power band (easier to ride), stronger than a 250 could ever hope to be! (Yamaha YZ250X or YZ250/450 FX bikes with wider gearing will be at a disadvantage)
-Off-Road (OHV areas), try to stall my bike you may not be able to! Want to ride Trials like for Extreme Enduro, no problem! (YZ 250 (non X) will have less top end)
Setup: Yamaha YZ ESR 325 - 2007 Model
-ESR 325, S7 Woods Porting, Silver Head, Race Gas Dome, (Use Race/Pump Gas 50/50)
-168 Main Jet (ESR recommended Main) and 48 Pilot Jet, Needle in the top position, may go to a 45 Pilot and change the needle position to minimize any unburned oil. Riding Altitude 500’ to 4100’
-Maxima Formula K2 Two Stroke Oil – Flash Point 240 Degrees (One of the Lowest) (helps reduce unburned oil) (40 to 1)
-No Fly Wheel Weight needed, but on the 250 engine a 9 oz. worked well.
-Rekluse EXP Core 2.0 Auto Clutch Kit
Summary: I do not work for ESR, but this bike is awesome! No more 250 for me! Dyno run coming in the future.
Attached Thumbnails

    212 Land - YZ 325 L side.jpg

Edited February 17, 2016 by SDTony 325

[218]

Did you compare the two CDI's to see what the X version brings to the mix? What spring and washer setup did you go with on the governor?

 

Good idea going with .040 squish and lowered compression. Must have had to take a lot of material out of that dome. Do you have any pics of the head?

 

Overall, what are your impressions of the ride now?

I have it set for the standard "X" spring and washer combo, but I haven't rode it yet. Hope to get out in the next week.

[rjpjnk]

Wow! Deep dome, flat top, maintained OEM wide squish radius. Was this head done by R&B?

Edited February 17, 2016 by rjpjnk

[218]

No. I did it myself.

[218]

The squish area is untouched. Stock angle and width. The dome area is basically "tubed" with a 22mm radius into the flat top. The gasket surface is shaved to get the clearance.

[218]

Got some riding time in over the weekend and I can't say that I'm thrilled. After riding a standard YZ for so long this feels a little weak. I'm pretty sure it's the PV set up that's bothering me. Running in the upper rpm just seems funny. When I back off the throttle and hit it again, it's like the power has to start over. Like it has to build back up to full power again. I'm use to getting out of it for a second and then twisting back on and still being in the meat of the power. Now I have to clutch it to get the power back.

 

Since I did all the changes at once, I'm not 100% sure what the problem is, but I'm leaning toward the PV spring. That will be my first swap. I have a complete stock YZ PV governor, so I'm just go back to the YZ unit and see if it fixes this.

 

I've built several lower compression YZ250's and they didn't act like this. They are smoother, but still YZ strong and pull out hard on top. This is something a little different. The CDI and PV governor are the only two parts that I've not messed with, so I'm thinking it's one of those. I may just swap CDI units, because it's so easy to do, and make sure it's not it. But, I'm leaning toward the PV right now.

 

Other wise, it pulls real nice from down low and seems to pull higher gears better. Very smooth. Reminds me of a '99.  

 

I think I'm going to race it Saturday just the way it is and see how it works out. It still runs great, just different than I'm used to and I'm a little on the fence about it. I need more time with it to figure out what's going on.