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How To Make A Yamaha YZ 250 Two Stroke Even Better

YZ 250

There is no question that the Yamaha YZ 250 is one of the best two strokes ever made. The Yamaha YZ 250 two stroke is reliable, affordable, fast, and handles as well as any modern ‘best of class’ bike out there. To this day, out of our entire team arsenal of motocross bikes, we still have the most fun when just ripping the track or trail on our trusty Yamaha 250cc premix two smoker. Two strokes are far from dead, and have even begun to show a noticeable comeback and stronger purchase demand. Not only are ‘two stroke only’ classes being added to race curriculum’s across the country, but two strokes are no longer virtually extinct from starting gates in modern classes, except at some limited professional supercross events. This year there were dozens of extremely successful two stroke venues gracing the pages of motocross publications. At the 2013 Loretta Lynn Amateur National Motocross Championships, the smell of premix was in the air and many front runners were giving chase to four strokes…if not being chased by four strokes. Several podium celebrations were rolled up onto with two stroke machines.

The Yamaha YZ 250 has been around and is as close to the heart and soul of motocross as you can get. Though the YZ 250 is almost unchanged since it’s aluminum frame arrival in 2005, it is still to this day a highly competitive machine, even in ‘bone stock’ form. There are however a few tips and modifications that can possibly make the YZ 250 an even ‘better’ ride. As demand for the classic bike increases, and prices rise nationwide for good used YZ 250 models, we thought we’d take a moment to share what we did to one of our very own ‘Team Chronic MX’ YZ 250′s for improved performance and durability. Some of our modifications may of had a slight ’bling’ factor, but most were to make our YZ 250 better than stock. The YZ 250 is such a great overall bike, that rather than parting with our older 2005 model…  we chose instead to give it a “makeover”, and forever keep it as a proud member of the family. After performing so many costly top end and valve replacements on our four strokes, our relatively inexpensive YZ 250 has been providing smiles, and even some podiums, all year long.

Here is the list of modifications we did to make our YZ 250 better than ever, and 100% dialed in. Not only did the bike perform better out on the track, the project also gave us a great excuse to enjoy many late nights in the workshop, listening to our favorite tunes! Cheers, Chronic MX.

Upgraded the stock Yamaha 2005 AOSS front forks to a newer improved pair of 2007 stock Yamaha SSS forks
Installed stiffer Factory Connection 5.0 rear shock spring
Installed stronger RG3 Triple Clamps
Performed Pro Action full suspension ‘re-valve’ for 175 lb A rider
Installed Scotts steering damper (Base: 8 out / high speed: 1 turn out / sweep: 9 O’clock for SX, 12 O’clock offroad)

Modified top end via BPM Racing Engines polish and port job (by George Babor)
Installed DEP exhaust pipe with FMF Titanium 2 silencer for better powerband and horsepower increase
Installed James Dean JD jetting kit (Main Jet 175, Pilot Jet 45,  Red needle / Clip 3 from top, air screw 1 out)
Replaced stock filter with Twin Air dual stage air filter
Installed V Force 3 Reeds for increased low end response
Added Steahly flywheel (9oz) for better traction and bite, less spin
Installed Barnett Clutch kit (with stiffer springs)
Installed Moto Hose coolant hoses

Replaced stock handle bars for stronger Pro Taper ‘Reed-Henry bend’ (w 800mm, h 92mm, pull back 57mm)
Installed longer lasting, better grip SDG seat
Added Acerbis Handguards for roost protection
Replaced stock plastic for Acerbis, with upgraded modern front fender
Installed stronger DID ERT2 gold chain (114 links)
Upgraded to stronger Renthal Twin Ring 51T rear sprocket (added one tooth for better gearing)
Installed Core Moto stainless steel brake lines
Added stronger Works Connection clutch perch
Added Works Connection skid plate, brake caliper guard and radiator guards for protection
Upgraded to better Braking oversized front brake disc rotor (270mm)
Upgraded to DNA black rims with blue hubs (bling)
Ride PG Team Chronic MX Graphics to’represent’
Seal Savers installed on forks during gnarly conditions for fork seal protection
Installed stronger Barnett Clutch Cover
Installed P3 Composites Pipe Guard for protection from rocks
Installed Steg Pegz for long enduros

Set Up
(Note: These are base settings, rider specific, and change frequently depending on track, condition, skill etc)
Fork Compression 12 clicks out
Fork Rebound 10 clicks out
Shock Compression 11 clicks out
Shock High Speed Compression (1.5 turns)
Shock Rebound (10 clicks out)
SAG 102 mm
Fork height 5 mm up
Fork springs (stock .44)

Amsoil Dominator two stroke oil (40:1 pre mix)
Amsoil synthetic engine oil (10W-40)
NGK iridium spark plug BR8EGV
Dunlop MX 32 front and rear (sand) Dunlop MX 52 front and rear (mixed hardpack)

DSC_6289 (Large)

Comments (15)

  • andre Smith

    I do social riding with my YZ 250 2t.

    How many hours before I need to replace the piston ?

    • Chronic MX

      As a rule of thumb, most professional mechanics will tell you that its a good idea to replace the top end on your two smoker every 40 hours…’top end’ meaning the piston, rings, circlip and even the pin. However, if you are an ‘easy rider’…keeping that ‘scream’ on the down-low…then you may want to just carefully inspect the parts mentioned to determine replacement. You may get away with just a new set of piston rings (or ring if only one is used). Look at the piston and inspect its sidewalls. Inspect the top too. Wear is not necessarily always just from keeping it pinned…a dirty air filter can sometime allow dirt into the engine, scaring the sidewalls of the piston or cylinder even on a mellow ride. So the key is inspection…if you see excessive wear, throw a fresh new top end in and your scoot will love you. If little wear is noticed, a new set of rings may be enough! Note: always use fresh gaskets, and check the wear of the piston bearing…if the top end is off and being replaced, then bearing replacement is also a good idea. Keep your filter clean and change oil regularly. Have fun Braaaap!

  • matt

    I have pretty much all of that on my bike.. 02 yz250. Except I run GP racing forks and racetech rear set for 210lbs. I’ve noticed its extremely hard to find graphics kits for these 2 stroke bikes.. I am using a 2013 front fender and stadium plate. Any ideas?? I like the gfx on that bike though!

    • Chronic MX

      Hi Matt, awesome that you are enjoying the trusty YZ 250 too. Sounds like your bike is nicely set up! There are dozens of choices for good graphics on this bike. A few companies we have used over the decade that did an outstanding job, and that we can recommend are 1. Armored Graphics 2. Powersports Graphics (RidePG) 3. Dirt Digits 4. Enjoy MFG 5. Stellar and more! All are well known in the graphics market and sell both proprietary and full custom kits. UFO sells the new YZ “Retro” plastic kit…so check them out too. Enjoy that ride! Cheers, Chronic MX.

  • Fernando

    What about for desert not just changing sprockets can i find a transmision like old wr 2 stroke that thing ran very fast

  • Dan Leigh

    Awesome write up, I too have a 2005 yz250 smoker and have 06 forks & triple clamps, Wossner forged piston, Wiseco clutch hub/basket, Talon front hub HD spokes, DEP front pipe, lots of anodized parts – the list goes on! I just don’t understand why anyone wouldn’t run the recommended 30:1 premix ratio. From what I’ve read about a guy with a dyno, nothing less gives you more power! Plus, using less oil may decrease maintenance schedule times. I’m not taking any chances

  • Omer

    Hey i have a yz250 05 i was just wondering what are the best brake pad to use (F/B)

    • Chronic MX

      Hi Omer… we have always had decent luck with stock OEM pads over the years. Depends on your brand. There are however many aftermarket vendors that sell high performance pads. It really depends on whether you are still using an OEM disc or not. “MotoStuff” sells one of the best discs/pads on the market… used by many of the pro teams! That’s what we use. Thanks and hope that helps, Chronic MX!

  • John Caird

    Hey guys, really excited to find this post I just picked up a 98 Yz250 that has been sitting for years and so I picked it up for a fun 2stroke enduro build and was looking for someone who has done something similar. To my surprise I found your post with everything I needed! I’ll be busting this thing out over the next 2 months thanks to your list of parts and company’s products. I will be making a video on how and what I do to it from start to finish on YouTube hoping it will help someone as much as your add helped me, I will be giving this post and your page full credit if that’s ok. Thanks again and I’ll post some pics of my progress.
    @John_Caird on IG come check out my page and build!

    • Chronic MX

      Good luck with the project John! Nothing more fun than a YZ250 screaming through a berm or down a trail. It’s a little easier on the pocket book vs a four stroker too. Our is still singing along! Cheers, Chronic MX.

  • Randy

    I was just wanting to start riding again, I rode 2 strokes all my life for the off road riding and I pay the price from a broke neck, ribs, legs and many others but I like riding more than anything but I have a small 2003 yz250 and I haven’t rode it yet bc I bought I used and I was wondering if I should go through it or buy a new 450f I have rode it and it has no top end speed from what I rode in the past like in 1974 I had a 2 stroke 450 Kawasaki I also rode the Honda 2 stroke 250 Elsinore but I am not sure where to go at this point should I put a new transmission and build that Yamaha or buy a 4 stroke that I never rode on the off rode before. I value your input on this matter because I still can ride like a bat out of hell and I need a pro input on this matter it would mean very much to my 58 year old man body with a boy at hart that wants to ride off rode again

  • zack gibson

    can you buy those graphics i would love to have those on my 97 yz250 thanks

  • Jeff Hubbard

    hey Zack, Factory Effex can do anything you want–>


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