2015 YZ 250F Big Bore Question

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7/21/2020 1:13 PM

Looking for some advice. Vet rider with a 2015 YZ250F with 110 hrs on it. Love the thing. Suspension is great, handles good, enough motor for me and reliable. Want to do a rebuild on it and possibly install a 270 big bore kit. I see there are full rebuild kits available with the stock bore. Is there a complete rebuild kit including all the parts for the bottom end with a 270 top end? Appreciate input..

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7/22/2020 11:39 AM

I believe you would go through like a wrench rabbit kit full engine kit, and get the cylinder works 270kit..

the 270 kit is freaking awesome. I love mine... im faster on it, and can rider longer than i was on my 450..

The power is ridiculous. feels every bit as fast as a 450 but with traction EVERYWHERE... on the 450 in corners segment 3, i was much slower than on a 250..

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7/23/2020 4:41 AM

TSCHAM101 wrote:

I believe you would go through like a wrench rabbit kit full engine kit, and get the cylinder works 270kit..

the 270 kit is ...more

Sweet thanks for the reply. Keefer did a test back to back with a stock 250 and a 270 and loved the 270 as well. I am 49, 6'1 205 and could use a little more to get over doubles out of corners. 450s are too much for me. I thnk i will pull the trigger!

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7/23/2020 5:57 AM

Ive been considering the same. Apparently the issue is getting a proper map. You can just easily buy the rest.

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7/23/2020 6:30 AM

I raced 270's and most of the tuners I asked told me that you can run most of the maps of the 250 with out concern. I was able to use the tuner on my 14 270 and had it running great.

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7/23/2020 7:39 AM

Schlava wrote:

I raced 270's and most of the tuners I asked told me that you can run most of the maps of the 250 with out concern. I was able ...more

I love my 250F. It has 108 hrs on the stock bottom end. The piston and cam chain was replaced at 90 hrs. Been remapped with the aggressive map. I wonder if the vortex ecu is really worth the money. I am a practice guy and want reliability..also not sure what would need done to the head as far as maintenance goes..

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7/23/2020 8:32 AM

Man that one guy is sure pumped on it, but really they're pretty much exactly what you'd expect from 20cc; a little disappointing. They gain a little torque, that's all. Nothing magical going on, but usually worth doing if you're not a revver. As with any bike, the more you weigh, the smaller the gain.

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7/23/2020 9:18 AM

byke wrote:

Man that one guy is sure pumped on it, but really they're pretty much exactly what you'd expect from 20cc; a little ...more

between this and getting my suspension valved are the best money ive ever spent on a bike.

and the Vortex is for sure worth it.. can get you almost 2hp on some bikes.

I had a built KX450 with linear pulling power.. and B Kit suspension. KYB AOSS forks..great bike, i thought i loved it until i rode a buddies built 250, and i was instantly faster, carried more corner speed.

and the engine work on the 250 to the 270 with a vortex and a port job were the single biggest improvement ive ever noticed on a bike.. it feels like a 450 power wise.. but it doesnt step out or want to come around on you, it has tons of traction.. pulls wheelies up Mt. St. Helens in 3rd, clicking 4th at the top. and im 200lbs..

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7/23/2020 9:23 AM

byke wrote:

Man that one guy is sure pumped on it, but really they're pretty much exactly what you'd expect from 20cc; a little ...more

I can see what you are saying, I am usually on the rev limiter only on a straight or landing from jumps. Definitely a lugger, Thats what I like about the YZ,it has bottom. I can think of a few tracks where there is a double out of a turn that if I dont hit the corner before it perfect, I will case the landing.. could use just a little more oomph. Since i am doing a rebuild anyway, why not unless there is something i am missing as far as reliability or problems go... What gearing change is required with a 270? Appreciate the responses.

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7/23/2020 9:32 AM

byke wrote:

Man that one guy is sure pumped on it, but really they're pretty much exactly what you'd expect from 20cc; a little ...more

TSCHAM101 wrote:

between this and getting my suspension valved are the best money ive ever spent on a bike.

and the Vortex is for sure worth ...more

I better do some more side jobs! $$$$. That is the biggest thing with a 450 is the inertia and the bike wearing you out. I just like the 250 better.

I wish there was a full rebuild (crank, gaskets, bearings etc) with a 270 cylinder kit included. Who did your motor work?? Has it been reliable?

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7/23/2020 10:22 AM

I will say this, I am too big for a 250f, however I hate riding a 450f because to me I am not as smooth and comfortable on them. We ride woods mostly.

I put a 290 kit in my WR and it is a beast with low and mid range torque, however it is dead on top end. Too me it is the perfect setup for the type of riding I do.

With that being said when I rebuild again I am going to go to a 270 kit as I think it will give me more bottom but still make sure that there is some top end available.

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7/23/2020 11:17 AM

Whats the horsepower difference in the extra 20cc?

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7/23/2020 11:26 AM

I've built a quite a few 270's, yzf and crf's with help from Derick @ HPbikes. All of these bikes run amazingly well with good reliability. Stock you will notice more bottom and mid with about the same top end maybe a bit more at peak. They don't loose top end power like most people think, what they may loose is some over rev from the heavier piston. Once you start building a 270 with more compression, ported head, exhaust and using a aftermarket ECU and tuned correctly they really come alive. One yzf 270 we built made 9 more HP at 10,500 compared to a new KTM. As low as 5000 it was 3 HP better all on pump gas. Still not near a 450's torque range but much easier to ride and less tiring.

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7/23/2020 11:28 AM

kb228 wrote:

Whats the horsepower difference in the extra 20cc?

Stock to stock about 1-2 more HP through out the curve.

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7/23/2020 11:44 AM

byke wrote:

Man that one guy is sure pumped on it, but really they're pretty much exactly what you'd expect from 20cc; a little ...more

TSCHAM101 wrote:

between this and getting my suspension valved are the best money ive ever spent on a bike.

and the Vortex is for sure worth ...more

Stevo683 wrote:

I better do some more side jobs! $$$$. That is the biggest thing with a 450 is the inertia and the bike wearing you out. I ...more

Twisted Development did mine..

And gearing i was trying to run 13-49. but im in between gears in corners.. im going 13-48 for GH, Elsinore and Fox, and probably 13/50 for Statefair and have all the bottom in the world for the tight tracks.

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7/23/2020 12:30 PM

NoMuff2Tuff wrote:

I've built a quite a few 270's, yzf and crf's with help from Derick @ HPbikes. All of these bikes run amazingly well with good ...more

That's amazing increase! Whats a ballpark $ wise to do a motor with a kit, and ECU?? I am wanting to do a crank for the hrs on it. Still runs great and has good compression. Thanks!

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7/23/2020 12:34 PM

Photo
This is a yzf 270 build on a conservative dyno anyone can build with a ported head, exhaust, 14.1 comp. out of the box cylinder works 270 kit with .010" cut off the base, GET ecu on pump gas compared to a stock KTM. I was hoping the peak hp would have been a little higher but a reliable motor with a broad torque curve was the goal. On Pro 6 fuel it rips on the track with plenty of bottom and mid power and still revs out like a high revving 250 and by no means is the KTM a slouch.
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7/23/2020 12:57 PM

NoMuff2Tuff wrote: Photo
This is a yzf 270 build on a conservative dyno anyone can build with a ported head, exhaust, 14.1 comp. out of the box ...more

Stock cams and valves? That's what I am looking for is broad power with good reliability..

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7/24/2020 3:28 AM

Stevo683 wrote:

Stock cams and valves? That's what I am looking for is broad power with good reliability..

No, sorry I forgot to mention the cams, the valves are stock Yamaha. It has mild Jesse Williams cams, nothing radical that takes a lot of spring pressure. I also forgot to mention it was dynoed with a brand new O-ring chain that definitely hurt the power out put, if I had to guess between 1 and 2 HP on a 250f? Maybe other guys know the HP drop from o-ring to non o-ring on a dyno. I'm not actually sure how much HP they rob. Those things are stiff as a board though. lol The owner didn't realize he had ordered a o-ring chain and since it has been replaced with a non O-ring.

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