Hey Guys,
Im looking at moving away from my 23 yz450f to a 24 yz250f. As I get faster on the 450 I feel there is a fine line to ride before hitting that 'oh shit' moment, plus I miss throwing around a 250.
I went to the 450 because I liked how connected the power was to the ground. I also didn't like how much I had to shift & the power delivery on my Honda. I really had to be in high rmps for my 2020 crf250r (Tokyo mods motor work), and thats not my style (I didnt spend much time on a 125 to ride a 250 like a racer).
Heres my question - Im looking to pick up a 24 yz250f but I am trying to think 2 steps ahead - I want to build the power similar to a 350 to have some recovery if I come into a corner a gear high and set up the bike so i'm not constantly shifting like a 125 (I know 'Get a 350 if you want 350 power', I just really love the new yz platform). Does anyone have any recommendations for port & Cylinder work? Is this the right direction to go? Whats a ball park cost of this kind of work?
Im located in Denver, Colorado - So if anyone has a guy/shop who they recommend i'm all ears! Thanks
Why not big bore the 250?
I'd call XPR and Twisted Development (TD) and explain what you're after and see what they recommend.
I know near us in Colorado there is a guy named Bruce (?) Sass, but I think he's retired. I understand he does still do work by appointment, however.
That said, XPR and TD are super tuned into the latest bikes and what you're seeking.
Start with the vortex or GET, and clutch assembly. Then you can add a second injector, before opening up the engine. If you start doing internal power then you need to address the cam chain, and rod to beef up the reliability to add the power internally. Just my .02
Bundy built seemed to be doing a lot of work on some fast kids YZ250Fs the last few years. IMO I’d strongly look towards the 350, a 250 with motor work is going to require a significant amount of maintenance and attention compared to your 450, and you still won’t be anywhere near the 350 as far as overall power and engine characteristics. A 350 w/ a Vortex and suspension work would be a much more reliable and fun bike to ride coming off the 450. If you’re looking for more power in a 250 I’d look into a big bore before actual motor work. Just my $0.02.
The Shop
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Bundy Built (JGR motor man) here in Charlotte is an east coast alternative
I'd be inclined to do big bore it and engine mods. I guess the yz crankshaft is the weak link. Would have to consider upgrading the crankshaft.
I bet in the end it would be a sweet bike and more reliable in the end. Long time ago bud did the 290 kit to his 01 yz250f. It was very reliable had it for 4.5 years.
I'd still like the option to race in the 250 class! Not a huge deal as I could always race a in 450 or a 25+.
Thanks! To my understanding the updates on the 24 engine were a beefed up cam chain?
The biggest issue I have with the 350 is the suspension. I've looked at them A LOT, but im not a fan of the rider triangle, chassis feel on the 23, and air suspension(I would immediately do a spring conversion which gets expensive quick, especially when most everything I have on the 450 will switch over to the 250).
Yes, but when adding power they still have “some” issues. You will gain quite a bit with the vortex and your typical mods like the twin air air flow kit and 2nd injector. It responds well to that. But when you go internal you start on a different path and imo it is always best to slowly piece together your final package to understand exactly what you are after.
Sweet, that makes sense! I know Twisted Development came out with an airbox/Vortex kit to help with some bottom end - has anyone heard about/ tested this (I've watched the Motocross Action video on it - seems to be solid but curious on that vs second injector)?
I've had great luck with the combination of a cylinder works big bore kit and the GYTR head on yz250f's. I've had this combo on my 2021 for years and before that did the same to a 2015. I go to an aftermarket clutch when I do it, but I'm a clutch abuser. Other then that I have not ran into any reliability problems. Solid power, that still runs on pump gas and isn't relying on more rpms or anything. Its power is not a 350, but its alot more then a stock 250.
As far as the cam chain goes, yamaha beefed it up for 2024 model, but I don't know that there is enough data to say how big of improvement it is.
What class do you ride on the 450 vs what class will you be riding on the 250F may help decide what mods to do.
4 stroke motor work is a lot more expensive than an air-to-spring conversion. If you’re looking to retain a stock bore with a 250 and get yourself a built motor I highly suggest dialing up 3-4 well known builders with all of your questions. A 250f with a built motor is a lot of upkeep and a lot harder to resale on the private market.
Some people won't like it but of course yours is a smart answer.
A 350 with suspension work, if the greatly improved recent KTM suspension is still not up to someone's standards, is still gonna be priced the same as a 250 with worthwhile engine work and the maintenance will be easier on the wallet.
The YZ250f I rode seemed to be geared fairly short. There was a lot more shifting than on a KTM or newer Honda.
Internal gearing or sprocket(s)? I run a 14/ 52 on the 450 now and know you can do the same on the 250f (I know its uncommon, but it made a big difference on the 450, the bike settled better on decel and into the corners and 3rd was usable in more places)
Just glad he's not selling shoes any longer...
Pit Row
You can stretch it out with different sprockets, but you will probably not be able to use 3rd in corners if you do. KTMs ship with 14/51 sprockets. If you put a 13/49 on a KTM, 2nd and 3rd are close to the Yamaha. The KTM/Kawi/Honda have much higher rev limiters so you can leave them in a gear a little longer.
I had a BB 250F and ran ~120 hours per top end, the only thing that was ever out of spec was the wrist pin. They tend to gal the chrome plating, I haven't had one of the newer engines apart with the DLC coated wrist pins yet to see if they last longer.
In my opinion, going with a BB, fuel tuning, and cams shouldn't require anymore maintenance than a standard engine. Especially if you don't get crazy with the timing, I'd retard the timing a bit and it'd be a fun bike to ride/race on.
If you ever stop by the BB shop it’s in NASCAR central and his motors are well known in the up and coming future NASCAR stars amateur mini sprint racing using Mx motors. I usually drive up and drop off product a couple times a year.
Bundy is a guru. Lots of kids won titles on his engines.
While ya there drop off your suspension at Art of War. Jonny is the ex JGR suspension guy.
Correct
By bb I meant big bore, it was just a no name cylinder with JE Pistons.
I have access to both. 350 KTM XCF and YZ250FX with cams and 270 cc kit. The YZ250FX is a more enjoyable bike to ride. It handles better.... sets up for corners better. Yes, the 350 has more power for hills etc.. but it just not as fun.
Worked woth John at bundy built a couple times. Hes a great guy. When i was down at club and roached a head. He let me bring it in that day and had it turned around that day. Even threw in new flat top valves for his cost. All to keep me from losing a week of my 2 weeks down there. Cant go wrong woth his shop.
Now that is awesome
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