How To Rebuild the Top End on a Yamaha YZ250 & YZ250X 

Or just use an extension from above

When you have to change the valves and the pistons is that considered a “rebuild”??

@@jupiterjac6438 🤦🏼

Il faire le rodage...

😊​@@jupiterjac6438

You bet!

Glad it was helpful!

القياس من جهة الأعلى فقط .

I can neither confirm or deny. -Charles

That's what we like to hear! Glad the video helped and thanks for watching!

Yessir

We have it filmed and we're editing it now. Might be a couple of weeks before it drops! -Charles

@@rmatvmc sick! Thanks

@@rmatvmc any update on that video being released soon?? Thanks

That's what I did

If the heads are fine reuse them. If not replace. Allen bolts can still sieze. Lube the threads.

use a JP1, JP2 or JP3 screwdriver, stop using phillips and you won't strip your screws anymore

Simple and easy to work on! 👏👏👏

There are a lot of variables that go into how long you can go between top ends but if you aren't racing you should be able to get 50-100 hours on a piston. A great way to know when it's time to replace the top end is doing regular compression tests. We have a great video on that that you can check out here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ui2cvCiGqA4.html

No, always good to take apart the power valve and stuff every now and then though.

Yeah, we have it all edited and it should go live this week. -Charles

@@rmatvmc right on thanks man

The engine oil is the oil you mix with the gas. Transmission oil only does transmission and clutch. There is no filter for your transmission oil so change it often

What? There was oil in the crank case?

I saw that too...

Look closer, they are there, he just didn't say it.

It should be safe to run with that jetting. It really depends on elevation and temperature, as well as intended use (sandy hills etc.). I know that people have had good luck at sea level, 70-85 degrees, 32:1 premix ratio, with a 175 main, 48 pilot, N3EW needle 2nd position, and 1 turn out on the air screw. You might want to make adjustments from there. If you do, try one jet size at a time till it runs the best, then check your spark plug. Look at the porcelain by the center electrode. Ideally you would want that to be brown, black is rich, and white is too lean. Look up "plug chop" if you need more information.

@@rmatvmc Thank you very much, I will do some tests and look at the spark plug, good morning

@@Liliros Here is how I jet a stock 2-stroke with a carb. They always come from the factory set rich, to be safe in any air quality around the world. So if you are riding on a track (not wide open all the time), and your "correct" plug is dark, I start by dropping the needle one notch, (move the little c-clip on the needle up one notch.). One notch is a big jump, and it will clean up the plug and you will feel more mid range power with less/no drool out of the pipe of vent tube, also keeping your exhaust power valve cleaner for longer. The YZ is very rich, but if you think it is too lean in the middle, you can get little washers (or make them), to punt under the little needle clip, so you can drop the needle a half, or 3/4 notch for example. Once you have the middle cleaned up, you will use full throttle runs, up a hill (the more load the better, and a cooler day helps keep you on the safe side of ambient temps), to check the main jet. Make sure you are on the rich side for full throttle runs (and stock jetting should be, but may not be with come engine mods), with a dark plug. Them hammer it wide open up a hil for 30 seconds, and hit the kill switch (so lower rpm's don't darken the plug. Just check full throttle for the main jet). If the plug is darker than a light brown and a dry electrode, put in the next smaller main jet and test up the hill again. I have never had to mess with the pilot jet, (idle to /8 throttle opening) on a stock carb. after setting the needle and main jet. Now, the plug should be a light brown color, with a dry electrode and even some color change to a bit darker at the elbow of the bent electrode. The bike will no longer drool out of exhaust exits, it will pretty only smoke on start up for quick spell, the power valve will stay more clean, less sticky, and you will have gained about 2hp with more power across the usable curve and have a higher top rpm. If the plug turns grey or white, you went too far. Drop it in the middle, then test for the main jet works pretty good. I just suggest a colder day (more oxygen) and a good load to the engine to do it, and you should stay on the safe side of too lean for most conditions.

Also, if you do most nay engine mods or put on after market engine products like a pipe, you should re-jet the carb, especially if you had it set well, (on the edge). I am going to raise compression for one example on my YZ250 2-stroke, (use a older higher compression head, or lower the cylinder a bit), and that will burn better, and probably make the bike run more lean, needing a bit more fuel. You can get that older head (2011 or before I think. look it up), and get a good mid range boost and still run pump gas, or cut .0085" off the gasket surface of your newer low compression head to make it the same as the old one.

Thank you very much for your answer, I like to have my 2Ts a little richer, I have decided to mount the 180 main jet in winter without verifying the color of my spark plug

If you have all the parts and tools, you should be able to knock out this job in less than a few hours.

@@rmatvmc Thank you, not bad at all.

Check the markings and measure them. Did you watch the video? 😅 We show you how right here ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-hJJL5vhlmMk.html -Charles

@@rmatvmc thanks

I'm not sure what bike you're referring to that is a 250 wrs. But this video will apply for Yamaha YZ250 and YZ250X 2 stroke dirt bikes.

@@rmatvmc ok thx

Hi! Can I swap yz250r 2002 block & head to yz250x 2018??

I'm not sure on the hours, just going in to take care of the problem. -Charles

If you don't mind paying more and not have your bike for a while, having a shop do the work is an option.

Even easier! Less parts and air cooled. I don't know if you watched the 5 miles of hell series but Justin rebuilt his DT 175 top end on there and you can see what you'll be getting into. Between these YZ top and bottom end videos and your service manual, you should still be able to get it done no problem. Finding parts might be another story... -Charles

You don't have to if you are staying with stock parts. The parts stack has tolerance to be wide and safe, but usually run better after you tighten up the squish with mods. After that, you should check the squish if you change any parts that create the squish distance. They don't check squish during assembly at the factory. They know the dimensions and tolerances of the parts, (5 of them that create the squish clearance), and just pick them out of a batch of parts to put together. That is why stock squish is almost always on the wide side, and never too tight.

This is a blown engine repair.. Trust me, the work here and the price is like 10 times less than a 4 stroke in the same situation..

@@geopioneergsxr5357 I know I own both. This video is overkill though. Spray that power valve out with brake clean and keep it moving

I always thought 2 strokes needed more frequent maintenance but the work is usually cheaper.

@@Cornholio223 ALWAYS cheaper.

Lol I love people who speak out 🙌