2025 Yz 250t

Sock is a 7.0    Most/all of PC's jetting recommendations use the stock slide.

If you get a setting that works well for you, post it up. My '24 runs pretty rich, even on MXA's recommended settings (which are, by the way, the same as stock!) 

Have you guys tried changing main jet, pilot jet & needle clip position? 

The YZ250 has had a 7.0 slide since Clinton was in the white house.  😆  Not even an exaggeration.    You can also easily verify this by opening the carb and looking at the stamp on the slide.

Are you mixing at 32:1 and using pump gas?

That's probably why you're a bit rich. PC setting is to drop the main and pilot one size each (175/48) and they run C12 at 32:1

I have a bunch of good jetting specs for these bikes, It just depends on what you want to do with the bike. IMO, this bike should have come with a  #8 slide. It just makes everything cleaner and more responsive. 

A #7 slide is for sure the stock slide. 

MX only:

Needle--N3EJ in clip #2

Pilot--45, I like using a 48 pilot with the #8 slide ideally. It just has a fuller (more torque) feeling in the lower part of the power curve, that you may want when using the PC pipe.

Main---178

Power jet---40

If you are using the stock, uncut head, you don't need that much c-12, I only mix it at 1 gal of c12 to 4 gal of 93, and I'm using a 5-UP head(21cc) on my bike. The bike won't run any better with more c-12. The c-12 is just insurance from detonation. It does nothing for performance, but it does smell good.

I concur with @digger, I'm running something very similar...  (the 2002 YZ250 needle is good)

My first move on a YZ250 or YZ125 is always to cut the head down a bit.
On the YZ250 I like 0.45in squish clearance (stock is usually 0.070in up to 0.75in).
I aim for 19.5cc to 20.0cc total chamber volume for an aggressive delivery or 20.5cc to 21cc for a mellow delivery.

I'm running the Bill's pipe, PC silencer and VF3 reed system.

Fuel is a 50/50 mix of Trick 110 leaded and Ethanol free 92 octane pump gas at 32:1 Yamalube 2R.

#7 slide
1-5/8 air screw
45 pilot
N3EJ (2)
175 main jet
50 power jet

I'm sure you can do better with some tweaking, but that setup runs well year-round if I run good fuel.
We're in similar conditions at sea level and we had mid 90s temps at Washougal last weekend...  
I grabbed both holeshots and moto wins on the YZ250.


Stock jetting for USA / Europe:

First thing, check float level.

For sea level to 3k, summer time:

-48 pilot
-175 main
-40 POWER jet (this is the sauce right here)
-N3EW-3 (in conjunction with the 40 power jet. It's 1 size richer needle clip while power jet is 1 size leaner. This makes for an overall more balanced power delivery at all throttle openings)
-1 turn out on airscrew, but may need to play with it slightly depending on time of day/temps

In winter, 178 main is better, but I've just been running 175 year round.

32:1 premix. I run 1/3 race gas (1 gallon to 2 pump in 3 gallon can).

As mentioned above, get head cut or buy a shiny aftermarket one. Anther option is picking up a 2010 model head (they have higher compression)... I did that for a bit on my 2016 and it ran pretty damn amazing. The stock head just has too big a squish band.

When removing .025 -  .030" from the head, do you run into any issues with the pockets for the 2 alignment pins getting too shallow or the head studs starting to poke the insides at the top of the acorn nuts?

Yes, you have to make sure the two dowel pins don't bottom out in their bores.

you can shorten the pins or drill the bores deeper.

I've never had a problem with the acorn nuts bottoming out.  I run the OE copper washers and nuts.