1998 Yz250 Power Valve Diagram

Alrighty then, well, let's pick up where we left off, and that's disassembling the governor itself, and re-stacking of shim washers.

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 hope this helps, and remember, not for errbody. I got very good results, but there will be some people for sure that will say "I'd never recommend this mod" and that's perfectly fine, to each their own. This is for the people who are looking to change the power delivery and are dedicated to the old school blue bomber.

Again, I hope this info is well received, and to anyone who is willing to try it out, I wish you luck and hope to hear back with your input, good or bad. As well, I only posted my findings, and what I feel ACTUALLY WORKS, and if I did have any negative affects from this, I wouldn't have come forth with the info, and would have simply returned things to how they were.

Posted by: lucianoterbush.blogspot.com

Source: https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/Re-timing-the-YZ250-pv-governor,1380968