YZ250 and flywheel weight?

[s10gto]

Anyone run a flywheel in there YZ. Got a 98 YZ250 Gnarly pipe , Turbine 2 , V-force reeds. Its no woods bike ,but thats were I put her and she rips. Bought this bike new and so use to her I was wondering if it would be worth getting a flywheel weight to tune her better for tight woods. Like I said I have rid her since new ,but now all I ride is singletrack so was thinking a little more trackability wouldn't be a bad thing.

If you recommend a flywheel what weight oz.?

Thanks

[diymirage]

Bets way to make that a good woods bike is to junk the 250 and replace her with a kdx 220 mill

[s10gto]

Oh no I could never.... Got a KDX too so its ok to ride the YZ in the woods. That makes it Legal

[diymirage]

Fair enough...but just between you and me...if you were to accidentally forget to add oil to the gas for the YZ i would understand

[s10gto]

I don't think the wife would.... She would see right through that one.

HMMMM I don't have a 200....

[Marky360]

I don't like flywheel weighs it destroys your big end try different sprockets a 15 tooth on the front will smooth the hit 50 on the back will help that what I run on my 97 kx 250

[Goofaroo]

A flywheel weight would give you the biggest bang for the buck towards making it somewhat civilized for woods riding. It will smooth the power and make it far more resistant to stalling. You might also look for a bottom end from a WR model. That would give you flywheel effect, lighting capability, and a wide ratio tranny.

[Julien D]

I have ridden an older YZ in the woods quite a bit, before and after adding the flywheel weight to it. I would definitely recommend fitting the heaviest FWW you can. Made a huge difference!

[s10gto]

Thanks everyone! Just may try one. Like the idea of being more able to lug the engine. Sometimes first gear is to high geared for techical sections. Was thinking may help so I can use less clutch.

[fuzzy]

It won't kill your big end, it may just take a little longer to get there. I've seen reports of a stock WR radar'd at 90mph. These things have plenty of power to spare, and can be quite a tractor, but the tall first is in fact a challenge at low speed. I've always wanted a '98 so I could do a gear swap on it. That engine will take the 93-96 WR trans, but is in the newer, more ergonomic chassis. I think the stock WR FW is 10oz heavier than the YZ wheel. That should have a PWK on it as well, which would benefit from RB's carb mod, just like the KDX does.

[Goofaroo]

I ran a 1990 WR250R in the Best In The Desert series "back in the day". The WR tranny will give you a lower first gear, 2nd,3rd,and 4th are the same, and 5th and 6th are much taller. At the time, one of the dirt bike magazines did a test compating the top speed on the WR vs the stock YZ. As I recall, the WR topped out at 107 mph while the YZ could only muster 77 mph. Obviously 77 mph is more than enough for a motocross track but when you try to use one for a play bike they fall way short. There isn't much call for going 107 but the tall gears will mean that you can cruise pretty quickly when you need to instead of constantly trying to upshift hoping that another gear will magically appear.

[s10gto]

Always felt it could use a 6th gear. Back in the day I remember I would race my brother-in-laws 86 KDX 200 AC. I could beat him WOT but it was by maybe 2-4 MPH. In my woods now I'm luck to see 3rd.

Appreicate all the info. Glad I came here.

[zz3gmc]

WRs were 5 speeds. I raced a 95 and 97 in enduros. Even geared lower for our eastern tight woods I still hit a ICO speedo indicated 83 mph trying to make up time. She was a fast bike! The YZ makes a fine woods bike. The flywheel will smooth the power delivery some and help with stalling. I ran a 11oz on my 01 and 02 YZs. Sometimes I would use a Eline lighting coil on my 02 which would feel like it had around a 13oz weight on it.

[adam728]

I also recall the WR's being 5 speeds, with mid 80's to low 90's. I ran stuff threw a gearing calculator one time, and if I recall correctly, with stock spockets it needed to rev 10k to pull 91 or 92 mph. That's WAY into overrev for a 250.

Sent via morse code

[Goofaroo]

I was remembering incorrectly. Mine was a 1989 model and the top speeds were different than I recalled. Here's the cover of the Dirt Rider magazine comparison between the YZ250 and the WR model:

http://www.dadscyclemags.com/2011/05/03 ... cate-test/

It was a great desert bike and very reliable.

[zz3gmc]

I just rebuilt my old 02 YZ250 that I sold to my friend, and while the cases were split I put in a WR426 5th gear. You can install the complete gearbox from a WR400/426 into 99 to current YZ250 2 strokes. Seems to go on forever in 5th!

[frame maker]

Just to add a few more thoughts getting back to the flywheel weight issue, I asked my friend Brian Turfrey about adding a flywheel weight onto my YZ250 to smooth out the power. Here is his reply "Pull the crank from the YZ motor and add some tugsten weight at 6.oclock on both crank wheels. I hate the heavy flywheels. Add a 10 mm pipe spacer to make the head pipe longer for bottom middle power." In follow up emails I asked about why he didn't like the bolt-on flywheel weights and he went on about all of the bikes (including a KX250 currently in his shop) he has seen with destroyed bottom-end bearings on the left side. So the extra weight on the flywheel is a benefit, but the weight needs to be distributed between each side of the crank to avoid left side crank bearing problems.

(For those who don't know who Brian is, he was a mechanic and pipe builder for Kenny Roberts, Wayne Rainey, Eddie Lawson, and a few other people who have raced motorcycles over the years. He probably knows more about getting reliable performance out of 2-stroke engines than anyone else on the planet.)

For my situation, the more I ride my YZ the better I'm getting at throttle control and have taken the flywheel weight off of my to-do list. Now that I'm getting more comfortable with the throttle I actually like how I can spin up the rear tire when I want. I also like Brian's suggestion of the pipe spacer to bring the power band down. That would be an easy mod and has gone onto the to-do list.

[bcdonyo]

I'd call Rekluse or EFM a see about an auto clutch.

I had a '89 WR250 and a '98 Canadian WR250 and the trannies were great, I've read before that as mentioned above the WR 4 stroke gears work in the 2t but I think they got some changes in '99, you could cross reference part numbers to confirm.

[gsa102]

I had a 90 YZ 250, and raced harescrambles with it. IMO it lugged well for an MX bike, and didn't need a FWW. It came with a Bill's pipe, which may have made a difference. The shock and seat were poor and that's why I sold it.

Of course, it did not lug like a KDX, but it had way more on top.

[frame maker]

I had a 90 YZ 250... Of course, it did not lug like a KDX, but it had way more on top.

Yep. I just took my '96 YZ250 and my '01 KDX220 for a comparison ride today. I rode the same set of rough technical trails on both bikes to see which one I favored. (note: I've added a KX250 frontend conversion on the KDX which is a big improvement in handling in rough trails).

I'd sum up my conclusion exactly the same. The KDX has more low end grunt, but the YZ has so much more on top that is was very noticeable that I could shift less often and still stay in the power. Overall the YZ was less mental effort to ride and I could stay more focused on the terrain and less focus on hitting the shifter. The YZ does require more delicate throttle control which might be a detriment to some novice riders.

That said, I still had a great time on both bikes. The YZ and the KDX are both supper fun bikes, they just require a little different riding style.