250 vs 300 2 strokes

The 300xc is an offroad bike. It's not meant to be ridden MX. With that said, they're highly tuanble and can be very good on a MX track with a few adjustments. A 300xc should not compare to a 250sx in power delivery because they are two totally different bikes meant for different things.

Yes it makes sense. Most peolple I know prefer the 250.

As far motor is concerned, if there any differences between and XC and SX, they don't matter unless you're at a level where you're doing it for a living. Suspension would be all that really matters. But I agree with the OP about being torn between the two. I sent my old yz250 cylinder off to Eric Gorr to turn into a 300 and the bottom end was fantastic, but the free revving fun was gone and it bummed me out a little. On the plus side, it really is just a piston and cylinder, fairly inexpensive and quick to swap around.

That dude with the YZ big bore and the wrinkly seat cover will be by shortly to give you all the information you did and didn't think you needed to know.

I wouldn't put a 300 on any KTM but a 17 and up 250. Why? The vibration on the 16 and below is unbelievable. At least with the 17 - up you have the counter balancer which is awesome.

I built a modified 2013 300sx and the torque was great. But I had it built for torque and it would rev out pretty good with the bills pipe and silencer. The vibration was KX500 level.

With my 2017, I have debated recently doing the 300 kit, PWK and STIC metering block just because, but I damn sure the minimal vibration of the 250 though.

Thank you for the helpful replies so far. I'll give it some thought. It really isn't a life or death decision because I'm pretty sure than if I install a 300 kit and don't like it I can sell it and put the 250 jug back on. But it's nice to hear some other opinions. In fact, I just talked to someone the other day who took his 300 kit off because he didn't like the vibration (his bike is a 2015, so like mine pre counterbalance). Maybe I can buy his. But that's another issue - more vibration. I'm not too concerned about that though because I've never really noticed the vibration on 300s I've ridden except when sitting still revving them up.

We raced TM300 SMX's for the last 3 seasons.. and i have a2012 MX bike.. IMO the 300 is less frantic than a 250, nicer delivery and easier to ride

Frodad78 wrote:

That dude with the YZ big bore and the wrinkly seat cover will be by shortly to give you all the information you did and ...more

Frodad78 wrote:

That dude with the YZ big bore and the wrinkly seat cover will be by shortly to give you all the information you did and didn't think you needed to know.

...more

Dude this is the funniest shit I've seen on here in a long time. Thank you for the laugh

Love my 300 on trail and slower speeds. Has the low end torque 4 stroke grunt and power on top like a 250.

As many have mentioned here, the 300 (or similar) is absolutely amazing off-road. I started out with the 310 kit (74mm piston) from Eric Gorr on an older KX I had and it was a torque monster, but it definitely flattened out earlier. Could carry taller gears for moto, but it wasn't a power band that translated well to moto. Played around with retarding the ignition timing and that helped a bit, but the 250 config was better for moto. With that said, I could easily see a 300 working great for a beginner/novice moto rider. Good torque/good power that flattens out early.

Then, decided to go to the 327, which took the stroke from 72mm to 76mm. All necessary parts and pieces were sent to CrankWorks in Arizona to modify/balance the crank with the parts (piston/rod, etc.). Bike vibrated much less and had a more aggressive longer powerband. A bit more of a 250-esque hit in mid-range. Put a flywheel weight on it and relegated it to full off-road. A perfect bike for me off-road and reliable as well.

Bore it for more bottom, stroke it for more top. I had a 125, made it a 144, hated it. So much better as a 125.

MXA said the 300 “full race” was too much.
I’m pretty sure they prefer the EXC 300 jug on the 250SX. Tune from there.
They had some interesting results from different pipes on 300 conversions as well. - Where the power was focused.

Ted722 wrote:

As many have mentioned here, the 300 (or similar) is absolutely amazing off-road. I started out with the 310 kit (74mm piston) ...more

Ted722 wrote:

As many have mentioned here, the 300 (or similar) is absolutely amazing off-road. I started out with the 310 kit (74mm piston) from Eric Gorr on an older KX I had and it was a torque monster, but it definitely flattened out earlier. Could carry taller gears for moto, but it wasn't a power band that translated well to moto. Played around with retarding the ignition timing and that helped a bit, but the 250 config was better for moto. With that said, I could easily see a 300 working great for a beginner/novice moto rider. Good torque/good power that flattens out early.

Then, decided to go to the 327, which took the stroke from 72mm to 76mm. All necessary parts and pieces were sent to CrankWorks in Arizona to modify/balance the crank with the parts (piston/rod, etc.). Bike vibrated much less and had a more aggressive longer powerband. A bit more of a 250-esque hit in mid-range. Put a flywheel weight on it and relegated it to full off-road. A perfect bike for me off-road and reliable as well.

...more

Beginner/novice describes me quite well - 46 years old, 220 pounds, back into the sport for a few years, mostly riding a sand track. The extra grunt may suit me well.

MPJC wrote:

Beginner/novice describes me quite well - 46 years old, 220 pounds, back into the sport for a few years, mostly riding a sand ...more

MPJC wrote:

Beginner/novice describes me quite well - 46 years old, 220 pounds, back into the sport for a few years, mostly riding a sand track. The extra grunt may suit me well.

...more

Yes, 300's are awesome. At the very least you'll have the knowledge to help someone with their buying decision someday!

If you're looking for a little more TM like delivery, it sounds like the SX would suit your needs. Anything can be de-tuned / smoothed out with a gearing change, flywheel weight, ignition timing, or power valve adjustment. The XC would be mellower from the get go.

Not sure if KTM still offers this same kit with ignition kit etc., but MXA did a comparo a few years ago.
https://motocrossactionmag.com/two-stroke-test-we-turn-our-ktm-250sx-into-a-ktm-300sx-big-bore/

Cylinder: The 293cc cylinders are the same for the enduro (EXC-W), cross-country (XC) and motocross (SX) models, and they have had the same porting and specifications since 2009.

Cylinder head: There are two different cylinder heads; a slightly lower compression XC head and a high-compression SX head, which still runs on pump gas.

Piston: Like the cylinder, the flat-top pistons have been the same since 2009. Some tuners feel that the flat-top piston is better at controlling detonation and works much more efficiently with pump gas.

Black box: The XC and SX kits have different maps. The ignition for the SX kit is more aggressive (as you would expect).

Related question: Does the TM 300 have its own engine or is it as the others, a 250 engine with a bigger piston and cylinder? I don't know why but in my head I feel like the TM behaves differently to other 300s. I have no reasonable fact to back this up though

A 17+ 300 with a PC pipe and factory sound silencer, high comp head, Keihin PWK carb and a STIC metering block will have the bottom end of a 300 on crack, and the mid to top with awesome overrev of a 250 on crack. Its pretty much the perfect two stroke setup. Its lightning fast.

Ray_MXS wrote:

Related question: Does the TM 300 have its own engine or is it as the others, a 250 engine with a bigger piston and cylinder? ...more

Ray_MXS wrote:

Related question: Does the TM 300 have its own engine or is it as the others, a 250 engine with a bigger piston and cylinder? I don't know why but in my head I feel like the TM behaves differently to other 300s. I have no reasonable fact to back this up though

...more

Just the basics, it's a 72mm by 72mm using a bigger cylinder/piston just like the KTM300. Same crank across all models of the 250/300 2-strokes. Based on their 2016 manuals, it looks similar to the differences between the KTM250 XC/SX 300XC and 300SX kit (partially).

TM changed the head, cylinder, and power valve assembly for the 300. Doesn't look like there's a different MX specific head for the 300MX, but each model on the TM has its own CDI. EN250/300 and MX250/300...so 4 different CDI's spec'd for each model exclusively.

Other differences look like internal and final drive gear ratio changes between the Off-road models and MX models.

Could have overlooked a part or two, but here's the source. http://tmracingmotorcycles.com/support/parts/.

Frodad78 wrote:

That dude with the YZ big bore and the wrinkly seat cover will be by shortly to give you all the information you did and ...more

Frodad78 wrote:

That dude with the YZ big bore and the wrinkly seat cover will be by shortly to give you all the information you did and didn't think you needed to know.

...more

Stuntman949 wrote:

Dude this is the funniest shit I've seen on here in a long time. Thank you for the laugh

Stuntman949 wrote:

Dude this is the funniest shit I've seen on here in a long time. Thank you for the laugh

...more

Haha..Like clockwork right?

Although I think he's called my bluff!!

I've got a 250sx and have spent considerable time on a big bore YZ with the Athena kit. I much prefer the 250. The big bore feels hectic and doesn't have enough top end. Also, the bottom end power isn't really that useable.

That being said, I'm 5 foot 7 inches / 150lbs so I just don't need more power than the 250 delivers. My buddy who owns the big bore is 6ft 3 and built like a brick shit house. He loves the big bore.

So there you go.


p.s. We had a hell of a time getting that big bore dialed in. Ultimately the it was a timing issue.

I've got a 250SX and honestly have never felt the need for a 300. My buddy just got a 2017 husky 300 and my 250SX can still beat him in a race (until I run outta gear). He has about 60lbs extra weight on me though). The 300's are just more mellow, less exciting and have more low end than i honestly need.

At this point in my life, if I wanted "more" I would just buy a 450. I would want something that clearly has more everywhere. If its a two stroke, I still like the 250's.