Hey guys, i snagged a used 24 yz250 2 stroke last week on marketplace. i havent been on 2 stroke in years besides riding my sons 65/85's and wifes kx112 as a pitbike at some races. Im tearing this one down to the frame to do a build. it wont be anything crazy but i figured while i have the engine out for the frame and everything getting freshened id do the bottom end. previous owner said the bike has 50 hours and 10-12 hours on the bottom end. Ive learned to never trust anyone so im just going to do it myself.
Now the reason im here. i want to swap a different head and just get a little more HP out of it for the heck of it. i am a bigger guy and have been on a yz450 for a cool minute but with how little i ride these days the low end torque just absolutely rips my arms. What heads do you guys like? i dont have an issue running race fuel as i barely have time to ride anyway with my son racing. so i wont be spending large amounts on fuel monthly for it. Any advice? can the stock carb perform well from jetting with head mods? Google doesnt seem to answer some of my questions.
I hear people polishing their transmission but where are they sending them out to do that? is it worth it?
also front brake setup. this bike has arc levers and stock line and caliper. first time with ARC. the flex feels super gross. i think its coming from the lever itself. ive only taken it up the street once the other day but i immediately didnt like it.
1. Hitlis Powervalve system. When you order it ask him about recommendations on jetting. He will set you up. If you decide to go with a head, then Apex is a great option.
2. The bottom end? Yikes. I sure hope not. If he replaced the bottom end at 50 hours then he royally messed something up. Are you sure he didn’t mean he replaced the top end? That would make more sense.
3. Polishing transmission? For what? So it shifts smoother? That seems highly unnecessary especially since you seem to be a guy who just goes out and rides around for fun every once in a while.
4. Throw on some stock levers and try them. I don’t have any experience with ARC levers, stock are fine, but if you’ve got money burning a hole in your wallet then Flo levers are very nice.
-For the head mods, I would measure your squish and then send it out to have it properly cut, and let them know what kind of fuel you want to run and they can also set up the dome for that. Having squish properly set makes it much easier to jet and it runs cleaner. I have two heads for my yz250, a high compression one for C12 fuel, and also one for pump gas just in case Im in an area where I can`t get race fuel. I love the C12 head, the bottom end and extra pull into the midrange is so nice for us bigger dudes (Im 220lbs).
-Also timing is big on these motors, you can retard it a few degrees and it will smooth out the powerband and also lessen the chance for detonation. And likewise you can advance it a couple degrees if you`re on tacky dirt and want some extra punch, but be careful of detonation if advancing. Get a dial indicator that screws into the spark plug hole, makes it an easy job.
-The stock carbs on these are amazing, once you have the squish set they are easy to jet so I definately wouldnt spend money on aftermarket.
-As far as transmission goes, they are mostly fine but watch out for 3rd gear on these. The dogs like to wear on the corners and this will cause you to slip out of gear at the worst possible times, when your on the face of a fast jump or skimming whoops. It started happening to me at only 20 hours, and at around 40 hours it was the 4th time it slipped out and it was right on the face of a 100ft table and I had the scariest endo of my life but somehow saved it. Parked it after that and got 3rd gear undercut at a machine shop, and it was perfect after that.
He 100% said top and bottom end. My son races gas gas 65's and 85 so a bottom end at 50 doesnt seem odd to me. those 85s are going out around 40 hours for the faster kids. I still dont trust what people say though so im going to replace the bottom end anyway. i do all the work myself so im not out paying a shop ridiculous money.
as far as the trans just checking in since it already will be apart if it made a difference.
I would just set the squish, run pump gas, and get a STIC kit for the carburetor.
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- I agree to send the stock head and cylinder out to get cut. Tom Morgan has done mine but I have a goof friend use Tiesta Tuned with good results.
- The yz likes some race gas regardless so I would plan on a mix of C12 and pump.
- The brake one yz is just spongey from the factory. Going to a braided line and solid mount rotor fix a lot of it. You can also switch to a crf master.
What he said.
I've had a ton of YZ 250's. No need to polish trans. Just keep fresh and quality trans oil in it. Shift forks and third gear not the greatest, but the motor is solid.
Your head and jetting has so many ways you can go. Pipe, silencer and what type of riding are a big factor. This also will come up, 2-stroke oil. I always run 32:1 Honda HP-2 oil, BUT, the best oil to run, is the oil that you have the best luck with.
Throw the front master cycling away. YZ's always seem soft and mushy. I always run a CRF front master cylinder and new brake line, problem solved.
All my YZ's I run the WC clutch perch/lever combo.
Congrats on the new bike!!
Mototech in NH makes some sweet heads, or measure the squish and have your stocker cut. Brian at Mototech is a great YZ source. So is Tom Morgan.
Do your research on HItlis before you spend the money.
I have good luck with the stock carb, but have never tested anything else.
Stock front brakes suck. I would suggest a braided front line and a CRF Master Cylinder, along with a solid mount Galfer rotor.
I’ve had my YZ 250 since 2013. It’s a 2011 I bought with only 2hrs on it. Had a lot of parts on & off of it over the years. I’m currently running a VHM head. Had a Apex head on it before. Great product performance wise, but the anodizing faded pretty fast. Check out DRT heads. It’s basically the newer improved version of a Apex head. Get a Boyesen RadValve in that bike. Don’t waste your time with a air leaking VForce cage. I never felt a difference in power with the VF3 at all. I’m also running stock gearing, stock carb (jetted) with a GYTR fly wheel. It’s a great combo to run. I did a enduro the past year with it and my bike had plenty of low end luggable power in the trails if I needed it. Congrats on the new bike
Agree with the comments on the head and the Rad Valve.
All the info in here is really great. Once you either replace the head or get the stock head cut the only thing I would mention that I didn’t read above is to grab yourself a Suzuki NECJ needle(part number 13383-37FE0). I’ve found the stock carb to work wonderfully and jet really well/really crisp running that needle at about every elevation and temperature you could dream of. Enjoy that bike!
That’s one thing I want to order & play around with this year. No complaints on my current jetting, but if it can be better why not. Currently at 178 main, 48 pilot, needle on 3rd clip and 1.5 out on the air screw
Lots of good info here. I'd check out DRC heads that B-Rad sells or Mototech as mentioned. Setting the timing with a dial indicator can help tune the power delivery. I have mine set 3 degrees retarded and I don't feel any lack of bottom and it pulls to the moon. Stock carb is fine. DRT has a jetting chart to get you in the ballpark.
I would keep the engine totally stock. Most reliable , great power band and good low end.
Before you do anything, I would ride the bike a few times and see what complaints (if any) you have about the motor or handling. If you haven’t been on a two stroke in years then just blindly throwing parts at it probably isn’t going to get you to where you want to be, after a few rides you’ll likely be able to tell where you want to move the power around to or possibly it may be enough in stock trim. Same with any chassis mods, without shaking the bike down it’s impossible to go in any useful direction.
Aside from just freshening things up I would keep it stock for a bit, you’d be surprised how quick these bikes actually are.
Leave it stock. 50/50 race gas and pump gas. They absolutely rip.
OEM YZ levers are great and have good feel.
Stock engine and exhaust + gytr flywheel
+1 on the OEM levers, nice feel
If you are tall I really like the Flo motorsports down and back foot pegs as well as a tall seat. Also gytr flywheel.
6’3 here and I second the tall seat. Absolute game changer to get me comfy on it.
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Brian@Moto Tech is a thief that stole the design from Danecke(DRT) If you are going to buy a head, get it from the guy that put in the hard work.
I have a phathead with a new pump gas dome. Anodizing is removed off the head and could use a little elbow grease, polish it up or have it reanodized. Shoot me a pm if interested. Been sitting on my work bench for too long
If you only do one thing, I would replace the head. Makes a huge difference. Runs cleaner, much easier to jet. Must have mod in my opinion on any 1999+ YZ250
I’m an older vet rider but I put an Apex head with the mild MX dome on my 2024, so I could get away from running race gas mix. The guy at Apex is very helpful and their jetting recommendations were spot on. I’ve had a few YZ 250 tranny failures over the years, it’s the only model I’ve ridden since 2008. Usually like someone else mentioned, the dogs on 3rd gear wear and it pops out of gear. I talked with Tom Morgan Racing he re-cuts the dogs on new gears for about $80 a gear. I never pulled the trigger. I’d keep my bikes for 100 - 150 hours and at the most would have one failure per bike, so I always figured my rebuilt tranny would last.
Make sure its fresh. Start with fresh reeds and spark plug, (regardless of how good you think they look or how little time you believe is on them)
Check your plug after riding a bit (WOT in 4th gear then completely shut off throttle and hit kill switch... coast to your bike stand)
Run C12 with a reputable premix of your choice at 32-1 ie. Maxima, motul 800, Klotz super techniplate etc
Clean carb thoroughly and it would be wise to replace the seals with oem seals as well as any gaskets for the reed cage
Verify the air screw position, needle clip position and jetting sizes that they are close to what is supposed to match your pipe. Doesn't hurt have a few extra jets to go up or down for both pilot and main. A good tuned yz250 will rev snappy and crispy on the stand, and then 1up on the main from that.
If you're doing the top end, make sure the powervalves are cleaned, and not damaged. Also make sure none of the components are damaged, loose or stripped. Sometimes on yz125's there is a pin that is pressed into the holding side of the valve, and those can become lose and get caught up, I can't recall the architecture of the 250 valves
Check your gearing, if it's stock (14f 50R), it will have a strong pull and forward drive (feels fast)
If its a 13 front sprocket or bigger rear it will rev out a lil bit quicker but will feel easier to manage if you're trying to ride pipey
These bikes are REALLY good stock, and most pro's I know keep the motor very close to that. A lot of lack of performance issues I've seen have been from over looking the things I've mentioned above
Just get the CRF master. The other fixes make it just ok whereas the master alone makes it night and day better.
Forgot to mention this in my response earlier. Absolutley get the crf front master cylinder! Night & day difference in power & responsiveness
any certain year?
I did a full 2010 setup for mine
They all work, back to at least 2004, probably further.
Just don't get a knock off Chinese model for $40 on ebay.
My money. Pro Cricut Shorty, Stock pipe, VForce, GYTR Fly wheel, You win!
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