Posts
406
Joined
4/21/2019
Location
CA
Edited Date/Time
3/2/2021 9:26pm
Hello to all who read, and whoever owns a yz250, or even a yz250x, and are wanting better power delivery out of their Yamaha 250cc 2 strokes from 99-current, this modification applies to your bike. It isn’t very difficult, in fact, it’s incredibly straight ferwerds and the total cost of the modification is incredibly low as far as upgrades to power delivery go, and this will fill in the dip in the power curve. It’s evident on a dyno chart, the dip in power from right off idle, to the upper rpm range, is clear, and when your riding a YZ250, of any year 99-current, it makes for a harder to control, abrupt, power delivery, as you basically have to scream the engine to keep it pulling like it should. This style of power may seem fast, but it’s deceptively slow, if 4 strokes have shown the world of motocross anything, it is, that smooth, controlled metered power deliver is key for for speed, so let’s close that gap for the YZ250 a little. This should work with just about any YZ250, from stock to modified, a re-jet will be required, but not in the manner most would think, it’s the boost jet that needs to be leaned out, stock is rich, and the added velocity in the lower rpm range will pull a lot more fuel, if a rb designs side is in use, or anything leaner than the stock #7 slide, it will help, but, the stock #7 slide works absolutely awesome and gives very good throttle response, but does require a leaner pilot jet in order to get the off idle performance we are looking to achieve to broaden power delivery, and make a very easy to use powerband.
So let’s begin
Firstly, drain the coolant and drop the oil out of the bottom end, then proceed to remove the exhaust, the Kickstart, rear brake pedal, and put the bike on it’s side(fuel shut off of course, don’t be silly like me lol).
Once the exhaust is off and bike is on its side, remove the water pump, and the power valve side cover to get at the pv actuator arm and take the bolt out so the actuator arm is free from the pv shaft. Removing the clutch cover isn’t needed, but it’s much easier to manipulate and line things up upon reassembly, and the ability to move the clutch basket to get the pv governor gear to re-align into mesh with the rest of the gears. Then remove the outer trans case, and remove the power valve governor.
Once the power valve governor is out, the fun can begin, it’s an incredibly easy part to disassemble, just be careful, don’t loose your balls
. Compress the spring by bushing down on the ball/ramp assembly, and drop the locking pin out, the governor will come appart entirely with the pin removed, just slide everything off the shaft in order.
The stock YZ250 pv needle thrust bearing washers are 1mm thick, and the YZ250X needle thrust bearing washers are 0.8mm thick. (Tricky tricky Yamaha) these will be the washers you replace. Initially, I ended up using all 4 yzx washers, but found upon install, that the 0.8 washer made the pv actuator arm sit too low, and it applies too much tension to the spring initially, basically adding more tension to the spring that you just tried to remove tension from. My instructions will show the order of washers, and a stock 1mm thick washer will be put back into use, with 2 0.8mm yzx washers replacing the stock YZ 1mm thick washers, and the 4th 1mm washer is entirely removed and replaced by nothing. This accounts to a 1.4mm reduction in spring tension. Doesn’t seem like much, but it makes a difference.
Once the pv goveror is re-stacked and assembled just reverse process to install everything again.
Your going to want to order all the parts at the same time, the 2 yzx thrust washers, gaskets, and a #45 or #40 Boost jet would be great, #35 possibly if your planning on utilizing the stock pilot jet in conjunction with a kawi #8 or rb designs custom slide grind. It’s about a 9.5-10, I’ve had #7,#8, and rb slide, and measured the rb slide.
Part number for the yzx thrust washers is
: 90201-154F5-00
So let’s begin
Firstly, drain the coolant and drop the oil out of the bottom end, then proceed to remove the exhaust, the Kickstart, rear brake pedal, and put the bike on it’s side(fuel shut off of course, don’t be silly like me lol).
Once the exhaust is off and bike is on its side, remove the water pump, and the power valve side cover to get at the pv actuator arm and take the bolt out so the actuator arm is free from the pv shaft. Removing the clutch cover isn’t needed, but it’s much easier to manipulate and line things up upon reassembly, and the ability to move the clutch basket to get the pv governor gear to re-align into mesh with the rest of the gears. Then remove the outer trans case, and remove the power valve governor.
Once the power valve governor is out, the fun can begin, it’s an incredibly easy part to disassemble, just be careful, don’t loose your balls
. Compress the spring by bushing down on the ball/ramp assembly, and drop the locking pin out, the governor will come appart entirely with the pin removed, just slide everything off the shaft in order.The stock YZ250 pv needle thrust bearing washers are 1mm thick, and the YZ250X needle thrust bearing washers are 0.8mm thick. (Tricky tricky Yamaha) these will be the washers you replace. Initially, I ended up using all 4 yzx washers, but found upon install, that the 0.8 washer made the pv actuator arm sit too low, and it applies too much tension to the spring initially, basically adding more tension to the spring that you just tried to remove tension from. My instructions will show the order of washers, and a stock 1mm thick washer will be put back into use, with 2 0.8mm yzx washers replacing the stock YZ 1mm thick washers, and the 4th 1mm washer is entirely removed and replaced by nothing. This accounts to a 1.4mm reduction in spring tension. Doesn’t seem like much, but it makes a difference.
Once the pv goveror is re-stacked and assembled just reverse process to install everything again.
Your going to want to order all the parts at the same time, the 2 yzx thrust washers, gaskets, and a #45 or #40 Boost jet would be great, #35 possibly if your planning on utilizing the stock pilot jet in conjunction with a kawi #8 or rb designs custom slide grind. It’s about a 9.5-10, I’ve had #7,#8, and rb slide, and measured the rb slide.
Part number for the yzx thrust washers is
: 90201-154F5-00
Hope this is well recieved info
With the governor out, take a look at how the entire setup works together, where the thrust washers, and needle bearings are located.
Apply pressure on the ball ramp, to compress the spring, and remove the retaining pin so the entire assembly can come apart.
Once apart, splay the washers and bearings out in order, that they come apart, even use a parts diagram to assure yourself if anything happens.
In the next photo, I’ve placed the two 0.8mm washers under the two 1mm washers they will be replacing, and remembers it’s only x2 0.8mm shims, that will be used, with the 4th washer closest to the pv spring, being completely removed from the assembly, so only 3 washers will be re-installed.
Time to re-assemble, you will see my finger pointing out the 0.8mm washers under the stock 1mm washers in the pictures, leave the 1mm washer closest to ball ramp in its place, then place the thrust bearing itself on, then a 0.8mm washer, followed by the spacer.
Once the spacer is installed, place the second 0.8mm washer ontop, followed by the second thrust bearing, but no washer after that, simply replace the spring collar overtop of the thrust bearing, and prep to assemble the spring, the gear shaft, and ball ramp apparatus.
Place the spring on the gear shaft, and slide the thrust bearing assembly ontop, followed by the ball ramp.
Compress the spring to fit the locking pin into the gear shaft, and line up the groove for the locking pin, and release tension. Governor assembly is complete, and all parts are ready to re-assemble.
Overall, pretty easy to accomplish, and for the added power below peak hp/tq will be noticeable, it’s almost like it pulls the way it should right from idle to red line, and your clutch is probably going to thank you for the less abuse you need to put on it to make the bike come to life.
Now for the jetting, ideally, the boost jet would be the guy to tackle, but, I didn’t have the proper size, only a #35, so I combated this issue by cutting the pilot size down to a 42, my needle clip was raised 1 position from the 2nd to the 3rd clip, as the off idle performance was a weee bit lean with the 42 pilot, and I’d get a lean spike almost right away, if I had my choice, I would be using a #7 slide, in conjunction with a 45 pilot, and 45 boost jet, so I had to compromise. I will be changing the jets again shortly, but due to not having a boost jet to replace the stock with, I opted for the leaner pilot, this gave a lot of added snap right off bottom, but due to the boost jet, I’ve got oil build up coming out of my silencer, it runs well, strong, no hesitation hiccups, or bogs, too much fuel is still though. my mods so far consist of the stock reed block, matched to the intake block(kinda pathetic Yamaha, simple fix for more power), as well as another no brainer, removing the restrictor from the stock silencer, but that’s it. Beyond that it’s an entirely stock 21 YZ250 with an 11oz fww and a iridium 8 heat range plug for purchased upgrades.
While We’re here, the stock YZ250 silencer is possibly the most overlooked piece of the bike, in 2011 it’s perforated core size was increased from 26mm id to 30mm id piping, the bent section between the silencer body, and exhaust pipe didn’t change, but what this has done is moved the pressure purging point sooner in the exhaust tract, thus allowing for much more exhaust flow, and by simply taking a dremel and grinding away at the two fusion welds holding the baffle at the tip of the silencer, and removing the baffle entirely will give you a completely uncorked silencer, that will our perform just about any aftermarket silencer I have come across, fmf, pc, dr.d, bills, all use the same 26mm Id perf core. here’s the example, had my 2015 yz’s silencer still kicking around, so luckily me, my 21 silencer is still pristine, and waiting to be shortened and uncorked.
Wasn’t in the topic, but meh, it’s another cheap but affective mod, same with the stock reed block, can be done in only a matter of hours with a bit of dremel, file, and sand paper work. Simple, cheap power. Minus the cost of my dremel, the three mods will cost you under 50 northern pesos to complete. so anyone on a a tight budget looking for better power delivery, everything is listed is right up your alley, and entirely attainable, and zero internal work is required, these mods may not be for errbody, but for you older vet and trail riders, it will be a very welcomed addition as the bike will lug better than it ever has before, Smoother easier to use and less abrupt power delivery, it will carry 3rd way easier in low speed sections, and you won’t need to coax it to life as much with a stab-o-da-clutch. Well, this alll looks so freakin huge from my iphones tiny screen, so I felt like iv just published a small novel, but on a computer screen, it won’t have nearly the awe lol
Again, I hope this info is well received, and to anyone who is willing to try it out, I wish you luck
So I didn’t realize the 250x washers were thinner & another part to this mod. I guess in theory you could do it both ways to fine tune it a bit. Try it with a 1.4mm difference as well a just a 1mm difference. I’ll try it your way first for maximum effect to test how I like it & go from there. Thanks again 👍🏻
Thanks for reading
The Shop
1.0mm for YZ's and 0.8mm for the X models.
On the spring side you can do whatever you want to tune the power. Removing one washer on the X has become the more common mod because it requires nothing but the time to remove it. I originally spec'd the use of a single 1.0mm YZ washer for all models with the X spring and that's the way I set them up when I do one. Regardless, it is a mod that most people like no matter which bike they are riding.
Tim King covered the Power Jet mod on Thumpertalk also. It works really well with the Power Valve mod, also.
There is quite a difference in the springs. I tested them with a shipping scale, press and guage blocks when I put the yzx spring in my yz. Stock yz spring installed length is .640 with 18lbs preload. Full open is .190 more compression with 40lbs load fully open. The yzx spring installed length as delivered in the yzx is .672 with 19-20 lbs preload (tested 2 springs, they were different ) with 52-53lbs fully open at .190 more compression. The popular yzx mod of removing 1 washer gives a preload of 15-16 lbs. As you can see the yzx was set up to begin opening later than yz. The mod sets it up to open earlier than the yz. Of course you can set it up however you like with the available washers coupled with custom grinding the free length of the spring.
Is it possible to modify the older pre-2011 26mm core silencers to achieve the same results? Doesn't appear so.
Back to the YZ250 silencer though, the pre-2011 silencers will still benefit from removing the restrictor, it’s still a 26mm core, but the restrictor size is that of a 125, 23mm. once you dive into a stock YZ250, and realize just how corked they come from the factory, remedying the little things Yamaha still likes to do with these bikes, can be very cheap if you have the tooling to undo these restrictions, the three major points with the engine, well, let’s say four major points, 1st the reed block mismatch, second the silencer restrictor, those two are just mere unbolt, and work with a dremel, the third and fourth, are internal. The exhaust port, is more the major of the problems with the cylinder, as far as freeing flow up, and then the mismatch between the base of the cylinder, and the engine cases, there’s a rather large shelf, that causes the flow between the cases and cylinder transfer ports, to mess up as this shelf that hinders the flow of air and fuel going into the transfer ports. I ported my 06 YZ250 first, rode it for a while, and then did a full tear down after my reeds ate my cylinder and I wanted to put a new crank in as well due to unknown abuse, at which point I matched the cases to the cylinder. It made a huge difference, it had much more bottom end to offer, it felt smoother the entire rpm range, and the overal power gains, as I didn’t do any more work to my cylinders porting, were awesome. Rambled again, and off topic (slightly if you ask me, it’s allllllll related hahahahah) But if your trying to squeeze power out of these engines, it’s very easy to do, and even saying that, with my 06 yz cylinder, I did not alter any port heights, only removed the material from the exhaust port, and re-surfaced, and cleaned up the casting flaws. In the transfer ports. Just that alone is still going to be a very good gain in power. If Yamaha really did try and clone the 01 cr250’s porting like it’s been claimed they have done, then why don’t they run as hard and fast as a 01 cr250.
Please don’t jump on me, these are just rough pics of a friends cylinder I recently did for his 2013 YZ250, and I didn’t take any pics of the final finish, stupidly enough :/
Bottom end snap, but it’s going to feel like that, because there’s more power above off idle that the stock silencer robs, same with the power valve mods, it will feel like the engine doesn’t make as much top end, but it does, it only feels like it doesn’t because below peak numbers it has more power, making the climb in power less abrupt, and more linear across the range. I’d be willing to bet, that any exhaust pipe with a modded stock silencer will our perform the full aftermarket exhust system, MXA’s exhaust shootout for the YZ250 even showed the best results with the Scalvini pipe came with the use of the stock 2011+ silencer, don’t really like to go with all that much mxa says, but when it comes to data, they did their due diligence in that article. So if the Scalvini pipe came to life with a restricted silencer, imagine what it would do for numbers with an unrestricted silencer. All theory right, but from my findings from all my modifying that I’ve done through the years, I think I’ve developed a good science in my methods, I wouldn’t be stating anything I felt really didn’t work at all. I do plan on buying a motorcycle dyno in the future, but till then, my arse is my best weapon in the struggle for power hahahahaha.
Yamaha put the ring in the silencer stringer to again top end HP and have been using those for many years now. The 30mm core was used when they increased the silencer length to offset the increase in back pressure caused by the added length.
Removing the ring on any of them will give similar, but less pronounced, effect as a "shorty" silencer.
In a nutshell for 2 stroke exhaust systems: less back pressure = more TQ / low end power, shifts the curve to the left. More back pressure, more HP / higher end power, the curve moves to the right. That being said there is no free lunch so the trick is you try to design a system that works the best overall. Some will lean toward the low end & others towards the high end. I have had stock, Bills, DrD, FMF, HGS, DEP, cone pipe & PC & they all make slightly different power in different areas (but in that order LoL 😆)
Also, was there any porting done to the cylinder or was it a stock engine with just pipe and silencer setups? And with that being said, I will be doing some back to back testing between the pure stocker, and uncorked yz silencers I have, you have my brain engaged for operation on this one, lol, so much for pv timing, hahahahahahahaha. Let’s just get into it, there doesn’t seem to be a heck of a lot of attention on the thread so let’s run with it
Now the fmf exhaust hit peak numbers the highest out of any of the exhausts tested, and even though it didn’t make as much hp as the pc it has a much broader power delivery, also, the end cap of fmf silencers have the largest opening of any of the silencers openings that I have come across, which to me, would indicate why it hit peak numbers at such a high rpm, even higher than the top end pc exhaust, which peaked sooner than the fmf, and it does have a restricted end cap, not as much as the stocker or the the dr.d, but it’s there.
Now the Scalvini, ohhhhhh the Scalvini, how i love thee on my tc150 (08 ktm 144 engine swap) I have measured the pipe volume, As I have tested just about every pipe money can buy for these bikes, minus hgs, and dep systems, and if the YZ250 pipe is anything like it, it will have the most volume of any of the pipes, as my 150’s Scalvini, has the most volume to offer of all the pipes i did a water test with.
This also gives me the impression that the larger the volume of the exhaust pipe, the higher numbers it will produce. as it was tested, to be the highest number pipe, mated to the stock YZ250 silencer, it may have gave the highest numbers, but, huuuuge butt on this one, lol, it peaked at about the same rpm as the stock pipe, very very low in the rpm range, here’s the other butt, they didn’t test the same day, soo who knows if it’s numbers really ring true, but, they still documented the findings, and stated them in the article. Also giving me the impression that the stock silencers core allowed for the most numbers due to the 1st purging point in the silencer, but restricted it to the point that it hit peak numbers sooner than it should have, and didn’t have ample over-revv. I tested a few silencers with my Scalvini pipe when it was a ktm 144sx , and between the fmf ti2 and pc 304 not the r304, the fmf silencer felt it gave better top end being it was a bit shorter and the end cap itself was of a larger diameter vs the pc 304’s.
As much of this is purely speculation on my behalf, the info mxa came up with, well, it has to have at least some truth to it. they did the dyno pulls with each setup, and as much as I like to disagree with what they say about a lot things, a same day dyno pull camparison, I think would be pretty hard to mess up, (been wrong many times, and dined on my own words plenty) it’s purely controlled environment, but at the same time, who really knows what they did, I wasn’t there so I can’t even say TRUE ,With 100% confidence, all I can do is make a decision based on the information provided, in hopes that these guys didn’t pull a fast one on us and just published crap for shits and giggles.
But here’s the shit, WE HAVE CONFLICTING INFO!!! What you have stated with YOUR findings on the dyno testing that YOU HAVE DONE PERSONALLY!!! tells me that mxa is full of shit, (yet again) so here we are, smashing brains together, and I could t be more intrigued talking with you guys, it’s awesome, I love hearing points of view and findings, and why you run which setup for what reason, it makes me think, and speculate, and challenge what I know to better refine what I’ve learned. Thanks for the info, and I really look forward to reading more, it’s kiiinda late on the west coast, so off to bed I go, where are you guys from anyhoo, don’t have to be specific, I’m in the most southern part of west coast bc, on van island, and no, I don’t cheer for the damn Canucks, bunch of back swinging tools they are, and got fed up cheering for the losing team lol.
Check this post out for a comparison of the dep vs hgs. I have also run both pipes, the dep with the standard length silencer and the hgs with the shorty silencer. The hgs makes a little more power off the bottom and then really makes power through the mid. It's a smooth power and his up well then signs off a little earlier than the dep. I find I can short shift and use torque to pull out of corners or on long and whooped straights.
The dep has slightly less bottom and mid than the hgs but pulls forever up top. I don't think I ever found the limiter with this combo. This combo was also really smooth but you need to rev it to make power, no short shifting with this pipe.
Both fit well but the dep silencer leaked at the bottom of the canister and after the first ride packing was coming out. Bit of silicone fixed that.
Both pipes are better than the stocker from the mid up
Pit Row
But these just showed up for me yesterday, and I’m trying to find what year of bike they came off of, or did someone get them coated red?!?!?
Yzf-22mm triples, the missing piece of the puzzle for fixing the handling on yz250’s specially the 2015 and earlier rake angle of 26deg vs the 2016+ rake angle of 27.7 for the yz/yzx amalgamation.
My settings for clickers on my 15/21 Yz’s were 4 comp and 4 reb from full hard on forks, 6 out on low speed, 3 out on reb, and 7/8th, and I wish I had the ability to go stiffer, so ima have to do a fork oil blend between a 5/7wt maxima fork oil to bandaid the forks into stiffer valving, did this with my 07 yz450f, and it worked really well for not having to spend money on springs and re-stack of shims you get a stiffer fork.
Post a reply to: Re-timing the YZ250 pv governor