YZ250 into 250X, all you need to know - Dirt Bike Build 

thanks for helping out Scott! :) hope it will turn out great

thanks a lot for sharing Bill!

Eric Gorr was a bit of a prick to me on the phone years ago, (and was partly responsible for a broken cylinder that he modified),--so I modify my own engines (do it for a living). if you want very good low end power, try this. 1) FMF Gnarley pipe: (I would like to try the stock 250x pipe, as it is a lower rpm target pipe also.). 2) V-vorce reeds with no aluminum spacer: The stock reed stop plate blocks off the 5th transfer port tunnel about 50%, and the v-force reeds open earlier for more low end power. No spacer tightenes up the primary compression a bit, for a better hit. 3) Lower the cylinder by not using a cylinder base gasket, (must use a good sealer if you don't want any leaks, (3M 847 Nitrile high performance rubber and gasket adhesive" is awesome stuff for that job.). The lower cylinder lowers the exhaust port timing to better match the lower rpm pipe, and that is where the best power gains are made, (pipe matching the porting). The squish clearance is till about .048" (.040 is about the limit for a 250cc MX bike), and the higher compression will need 100 octane fuel. Strong off the bottom, can short shift with no clutch, and not fall on it's face (190 lbs and stock gearing). Not too abrupt though, just powerful and smooth. I don't think I need a flywheel weight. No charge.

thanks brother, hope so!

thanks man!

thanks!

cool! I would like to get steel frame later..

thanks Jake!

cool Andre, glad you like it!

me too, it will take few month tho.. hope this time I can do it bit faster!

great info, thanks a lot Newton! I will experiment with flywheel weight for sure

thanks for sharing Gabriel, I plan to use big rotor and braided lines for the brakes

thanks man, sounds like you have very nice setup!

Thanks bro, glad you like the videos. There are some difficulties on the builds, but once you overcome it the results are super rewarding. 😉

me too!! ;)

Thanks bro! That would be cool 😉

@@dirtniron Do you know where i can buy cheaper bikes from your place? im from the Philippines and I want to buy some Dirt bikes then sell it here or make it my project bikes.

i buy all my bikes here sandiego.craigslist.org/

sorry Ryan, you can look it up online quite easy. Use rmatvmc website

thanks bro, appreciate it!

glad you like it, I decided to not do FWW at this time

cool Philip, that is a really solid bike you will love it!

that would be great!

what other JP companies are making two strokes?

Yes i have around 20 videos total, go to my main channel page - yz250 build

Thanks Brad, yea it would be great to see Yamaha come out with full package, counter balancer too and maybe even 300cc engine. I bet lot of guys would get those bikes!

thanks Kirk, I will check it out

glad we could help!

I have a 2002 yz250 I've turned into a trail weapon:) Springs Clutch cable Clutch handle and perch Throttle tamer tube Bigger foot pegs Fly wheel weight Working awesome 👌

Yes Justin, i am going to get offroad suspension for sure. I will send it to racetech probably, they did great job on my ktm sx suspension.

Dirt N Iron fantastic. A Racetech certified shop did mine. It’s amazing.

thanks for sharing Tom, sounds like a great project. wow, you had a lot of fun early 80's, would be great to meet one day I listen to some of your stories. I was just getting born in early 80's. :)

I have a close friend that just finished a frame off restore on his '81 IT 465 that he had bored out to 490. Cool bike, a little scary, but still cool.

@@xterrential Sounds great! Yup....the '81 YZ had better forks but a tad bit tamer engine. If your friend has trouble with detonation there are head mods to increase squish that really help. Guys used to take the '80 engine and put into '81 frame or simply get triple clamps/forks for their '80. Those big YZ came on like a 125 if you got whiskey throttle.....saw God a couple of times riding in the mountains.....

@@dirtniron It was a nice ride....many times I was sorry that I sold it but as a fella gets older his bones don't distort like they used to do. With the IT cylinder you could "sneak up" on the power more and the wide-ratio trans was wonderful. I did some squish band mods on head that really helped. I'm 73 now and need a few parts(on me) to be able to continue riding. I put organ donor on my license but I don't think they'd find much they could use! No lie. Really enjoy your projects and envy the riding terrain that you have out there. Is that California? Keep the Faith, young fella.

@@tomnekuda3818 I will need to start calling you "sir Tom" :) I am really pleased that people like you are on my channel and enjoy the content, you have a lot of bike/life experience, it humbles me to know that you watch my channel. Thank you sir ;)

thats the plan 😂😂😂

@@dirtniron cool

thanks for the tip! appreciate it Brian

Apex technical innovation

Thanks, getting most of it for the build

sounds good! If you need to fix the radiators check ICW, he is magician ;) have fun!

@@dirtniron I already went to a local radiator shop and they said there was no hope. Oh well, it's only $400 for a new OEM one. Maybe I'll go for the $150 EBay special instead...

yes, from Canada called Panthera, its kinda pricey tho.. decided to stick with kick start only ;)

@@dirtniron well to tell you the truth I dont really blame ya because of the price its quite ridiculous

thanks! the intro is my friend's work tho ;) i think 125 is kinda small for me.. almost 200 lbs, plus I dont really know how to ride that thing, you need to be wide open most of the time I guess

@@dirtniron Well I rode a 300 2-stroke, then a 250, and finally a 144, and my 144 gets the most use. I ride at 6000+ ft in Colorado and weigh the same as you. I enjoy being on the pipe more and I find it easier to ride harder for longer. More shifting and some clutch work, but I find it the most fun. I also have found I am faster on it too.

thanks man! I did Eric Gorr 300 on my KTM, this time I want to keep it 250 and play with porting and other stuff

@@dirtniron I'm interested to see what porting mods you come up with. I have a 2002 yz250 2 stroke and I put a 13 ounce flywheel weight on it that drastically improved it's off road ability. However, with the 13 oz fww you have to bend the clutch actuator arm for clearance which wears out the cable quickly, so I would recommend not going bigger than an 11 once weight should you go that route. You do good work and this build will be entertaining.

The ESR 325 cylinder is steel sleeved and not nickasil coated. Big jump backwards in technology

i ended up using stock YZ power valve

yep, already done for my weight and skills for trails, Racetech did the work

this one should be decent too ;)

@@dirtniron I have no doubt, your builds are always top-notch! I just have a soft spot for the Yamaha ITs!

cool man, glad it helps!

tentokrat dam smartcarb, tlmice budu offroad komplet prestavba (racetech)m cdi je z X model, fmf gnarly a turbinecore2, IMS nadrz.. atd :) Dik Michal, drz sa aj ty!

thats a great encouragement Mike! glad you like the plans for my build, I will be checking your yz250 as well, you are way faster than me ;) trying to improve my video production step by step, glad you notice the changes. There are many channels with the builds these days, they do great job with builds and vids as well, good motivation for me, thats for sure ;)

haha, It's not a race! But for sure, hurry up! 😆

I got both heads modded by Tom Morgan Racing, one for pump gas and one for race gas

thanks!

not 100% sure, but think they are the same

yes, just change those 3 gears

hey Darcy, I spent some time on 2019 yz250f this year and its a great machine, you will love it. Here is the video from the track: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-gNUneAih-GY.html

interesting, thanks for sharing Mike! how does it feel now compared to how it was before

Really mellowed out that yz light switch. Power delivery a lot like the x now. Way more off road friendly

@@mikewatkins4512 do you have a part number for the spring

Ordered from rocky mtn atv, Oem parts

change the plug, check the carburator, try again , good luck ;)

Any year is fine, its the same as far as i know

not sure I understand.. what do you mean?

@@dirtniron reference of the parts mentioned on the video

yes, on the list! thanks Will

I am not sure, try to check the part numbers on 1999 yz250 and 2007 yz250

what exactly is it?

I can play with it as well

Yes

yes I heard that, but I am planing on getting gnarly FMF pipe anyway. Thanks for sharing

probably till 99 but dont quote me on that.. check thumper talk forum

I think so

Ankit Parikh the yz 04 and 05 engines are exactly the same

Dustin Jean Agreed everything is very similar except for the aluminum frame... which should make some difference, no?

Ankit Parikh ya the aluminum frame and the front forks are different to I believe, few mil bigger. The aluminum frame is stiffer which is better for motocross because it’s stronger more consistent feel on a track that’s why most new motocross bikes are aluminum frame however stiffer means it will vibrate more. Pretty sure that’s why euro enduros are all steel framed for more comfort in off-road, motocross needs the strength for jumping. So what’s better depends on what you like to ride. If you are a trail rider I would keep the steel frame, you want a better Moto bike I would look for the aluminum frame version.

Dustin Jean I’ve been riding motocross lately... so I just got this 2004 yz 125 and it seems like finding a 2005 yz 125 around Utah-Florida that I could affordably get would be hard... but not impossible. Idk if I should hope and hunt or just change the frame/shocks...? What do you think?

Ankit Parikh I don’t think the frame and suspension is night and day better than the 04 but it is still better. Depending how much and how comfortable you are with your current bike you might not even be able to feel the difference. However the 05 aluminum frame and suspension is basically what the new 2020s are so you would have the latest and greatest. You could also save the money and have a professional revalve your suspension like race tech and that would be better then stock 05 suspension. I think you have to be a pro to really benefit from the aluminum frame itself but it does look cooler and it is the most updated frame they made for the Yamaha’s 2 strokes

thanks bro, I like to set challenging goals, it pushes me to go further and work harder ;) they did not change much, with good suspension tuning, engine porting, oversized brakes and steel braided lines, etc.. we should be able to get somewhere ;)

do some research, there must be some sites shipping to Austria.. US has a lot of parts available

I think you would love the change. For me 450 is too much even for mx riding.

thanks for sharing, I did not know that. I will be getting full Hinson setup tho

i am not sure, but I will get mine ported

The exhaust is .5mm higher in the x.

yea, and 18 inch wheel.. but I was talking about the power/engine in this video

i am not a big rekluse fan..

That’s intriguing. Can you explain why that works so well?

good info Craig, thanks for sharing!

One other note the inside of replacement third gear was coated on. On the inside were the dogs lock in the stock one did not have this. That clearly tells us yamaha knows the problem..but why not fix it ? Mo money of course ..with no competion like a cr250 x 2st..there is no need ..

haha, I have different accent tho.. my friend is Italian.. they have different melody to their language. I am from Slovakia