Build my '15 YZ250 or buy a 125?

You should build your yz250. I know someone you can model it after!

Um shouldn't even be a thought as to which bike... 48mm SSS vs 46mm Kayaba's?

Best in the aftermarket industry goes to the YZ, if you can dream it someone makes it for the YZ. A great bike to make your own through the aftermarket.

Although the YZ's design is dated, it's light years ahead of what Honda was offering in '02. It's the definition of refinement in the MX world, quite the tried and true platform. Buuuut saying all that, I ride an RM to be different.

Keep yz. buy the 125, spend the $1050 on it and it will be in good shape

Good morning,
I have been in this situation and have some info that might help with your decision.

My current moto bikes are a 2006 YZ 250 and a 2006 YZ 125.
In 2006 I bought a lightly used 2001 CR 125, the bike was ridden by my friends wife and had no time on it. I pulled the piston out when I got it and it looked brand new, no carbon at all. I pulled the suspension off and had my local suspension guy set it up, he had done all of my suspension for 15 years. This CR 125 was the worst bike I have ever owned. The motor was extremely temperamental and the suspension was no better. We made adjustments over the next two years and the bike never came around. I sold it for $650, the bike was imaculate but just terrible to ride.

In 2008 i bought a stock YZ 125, sent the suspension to Enzo, freshened up the top end, and put a Hinson basket in it. It came with a Pro Circuit pipe. This bike is absolutely awesome. It handles great. Just hold the throttle on and use the clutch as traction control. I have never touched the jetting on this bike. It rips.

In 2013 I bought a 2006 YZ 250, sent the suspension to Enzo, freshened up the top end, put a Rekluse Z-Start Pro in it, Gnarly pipe, fly wheel weight, and 18" rear wheel. This is my woods bike. Again this bike is killer. The only issue I have with this bike is you have to be a surgeon with the throttle. I put a G2 throttle on it with a their mild cam and it still wasn't enough. I just sent the cylinder to Eric Gore and had him do his Mobetta port ($200), this should take some of that initial hit away. I am putting it back on the bike this week and will have a ride report shortly after.

1.) invest in a 125. Maybe a aluminum frame YZ125?
I wouldnt ride a CR again after knowing how good the YZs can be.

2.) invest in my yz250 to make it as fun as a 125 but a mean machine on the track.
A 250 will never be as much fun as a 125.

My budget is limited, like probably $2000? Although I could just pay the bank back LOL.
Hold out for the YZ125.
Get an over-sized front rotor kit for both bikes.
Ride...

The YZ125 is a far superior bike to the CR125... More than that, the commonality of parts between the YZ125 and YZ250 that you already own is a good thing if you're on a tight budget.

Hold out for a YZ125, find a good one and ride the hell out of it.

I second this.

Especially if you are on a tight budget. The parts swap is a for sure plus.

I had a 2002 CR125. The motor was weak even with the suggested 05airboot and airstriker carb tuned to perfection.

I also did not like the power valve set up, it is a crude design and pissed me off.

After owning a Yamaha with SSS forks, the Cr125 had not good suspension, I realize now.

Here's a better question, why have one or the other? Life's short have both! And definitely YZ, like everyone says, parts swap makes life wonderful

First up get yourself an oversized disc at least! a braided front line makes a decent difference also.
First and best mod I've done to most of my bikes.

ok so what do you want?
Scenario 1.
Coming into the perfect berm taking the wide outside line stretching the throttle cable with the 125 tapped out in 3rd, fanning the clutch and flat shifting into 4th, all the while smiling and having fun?

Scenario 2.
Comming in hot on the 250 square off the corner and slip the clutch and hammer out wide eyed into the next section all giddy inside??

The 2-stroke Yamaha brakes are plenty powerful, but the oversized rotor gives you more precise control, so it's a great modification for sure.

Get your suspension re-valved and re-sprung for your weight and speed before you put any money or time into engine mods. Keep up with suspension oil changes and set up your chassis to handle perfectly for you.

I'm pretty sure the '11 and later YZ250 came with a 49 tooth sprocket. I prefer a 50 or 51 tooth on most tracks with the 250cc engine and a 49 tooth with my 300cc engine.

The VF-3 reed adds a bit of mid-range that helps coming out of slower 3rd gear corners.

The stock pipe on the YZ250 is really good. The PC does get moving a bit smoother in the low/mid. The DEP pipe is the smoothest and also pulls stronger mid/top than anything else I've tried. I wouldn't spend the money on a pipe for a YZ125 or a YZ250 unless your stock pipe is beat up or you want the bike to look cool.

If you are running race fuel, don't be afraid to play around with your ignition timing on this bike to dial in the power.
If you want to shift the power curve down lower, advance the timing (move the stator-plate clockwise). If you want to shift the power curve up higher in the RPM range, retard the ignition timing (move the stator-plate counter-clockwise).

A head-mod makes the YZ250 run cleaner, crisper and more forgiving for bad fuel. They tighten up the squish band while maintaining stock compression ratio.

Either put a flywheel on your YZ250 to tame the hit a little or try to find a great deal on a 2006 or new YZ125. I'd avoid the clapped out Honda.