Improved low end and smoother power for 95 WR250

dog

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#1
I have been riding a 2 stroke WR250 Yamahas for years with good results. Recently, I rebuilt my 95 WR250 (same head design as the 94YZ250) and followed the recommendation in Eric's book for improved performance with a fresh top end, jetting changes, and Boysen reeds. I also put on a PC pipe with FMF spark arrestor. The bike makes major mid-range and top end power (one of the hottest 250's I have ridden), but for Enduro work the power is hard to control. I tried the PC pipe first because the PC pipe for my 93WR250 had a terrific power band with great low end power and a broad mid-range. I have used flywheel weights in the past, but this motor really needs more low end torque with smooth delivery right off the bottom. The bike is a perfect desert or outdoor MX bike in it's current form, but I mostly ride in the woods.

My question is: What should I try first?
1) A set of FMF torque reeds (that I already have a new set)
2) An FMF Fatty (that I already have a new one)
3) Going back to the stock pipe (which I have)
4) An FMF Gnarly pipe (I would need to buy)
5) Porting and power valve port mods (more money and down time)
6) Flywheel weight ( if still needed after I have more low end)

Thanks!
Kellsey
 

Lorin

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#2
A flywheel weight is a very good addition to this bike, as it mellows the hit considerably in the middle. I would spend the time\money porting the bike for bottom and go from there. One of my friends has a 95 wr that he had done by Emig racing (including the flywheel weight) that has a very linear powerband (read: almost no hit). It is kind of like riding a kdx with more hp. Not very exciting to ride, but very smooth, controllable, and solid power all of the time. With his mods, it is a hard bike to beat.
 

Farmer John

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#3
dog,
One of the very best things you can do to a 94-97 WR250 is a long rod kit.
It smooths the whole power curve out. Yamaha used to offer this in kit form. Consisted of a longer rod (same dimensions as an 89 YZ, I belive), two base gaskets, an aluminum plate for under the cylinder, a longer powervalve arm, and a longer right side powervalve cover.
 

wrench

'00 Flappin' Fender [Ret]
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#5
Mods to my bike for the woods

I have a 94 YZ 250, that is mainly ridden/raced in the woods. Here is a list of mods that have been done to make it rideable in the woods.

Cyl. Head = Squish band re-shaped (EGORR) to smooth out the "HIT". (also allows the use of "pump" premium)
Cylinder = Stock porting/Std. bore
Flywheel Weight = 11oz. Steahly (bolt on) to make the power delivery more "tractable" (lessen's the wheelspin off bottom)
Carb(MIKUNI/TM38SS) = 6EJ33-59 jet needle,#380 main, stock pilot (as per EGORR)
Reeds = Boyesen pro series (EGORR)
Pipe/Silencer = FMF FATTY/FMF Power Core II
Final gearing = 13/51
I run a premix ratio of 50:1 (Amoco93/Motul 600), and a B7ES(MXTUNER) plug. Even with these modifications, the bike is extremely fast on top. It now has better manners down low and through the midrange

I realize that you have a 95 WR 250. There are many similarities between the two bikes. So I thought that this info would be usefull.

wrench
 
Last edited:

dog

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#6
Does anyone have experience with FMF's Torque Reeds compared to Boysen's?
 

dog

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#7
Thanks for the info Wrench. The 94 YZ250 and the 95WR250 are almost the same bike. The WR has a little more flywheel weight and different gearing of course.

An update:
I switched from a Pro-circuit pipe to an FMF Fatty, still using the FMF Turbine core II. The power is a little broader with the FMF, but I would still like having some smoother power right off the bottom and up into the mid-range. The bike is still a handful in tight woods and slippery conditions.

Maybe I will try a Steahly flywheel weight again.

Does anyone have comments on the FMF Gnarly Pipe compared to the Fatty?

How about other comments on cylinder porting to solve the problem?

Thanks!:think
 
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#8
My '95 wr250 was very smooth on the bottom to midrange. I had Boyesen power reeds stacked over top of the stock ones(mistake) and it smoothed the big hit out really well. A 12 oz flyweight, forget the reed spacer.....it didn't help mine at all but did move the carb boots enuf to make them slip off once in awhile. I installed the '97wr250 ignition which let it carburet a little better and also smooth out the bottom power. This is the same ignition as the same model yz250...the spark mapping is different...allegedly. I had a fatty pipe that seemed to help mostly from mid to top while the stock pipe will make it nastier on the bottom end. Adding an FMF S\A also helped smooth the hit and lengthened the lowend pull into the midrange. The bike was a yz4 eater and could put almost any 4stroke to shame in slow going. A truly versatile ride.
 

dog

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#9
The solution to my question on this thread turned out to be the FMF Gnarly pipe. The Gnarly (Torque) pipe made a huge improvement in bottom end torque and the ability to ride the nasty off-road stuff. This made the power very controllable. THe FMF fatty would be a better choice for desert or fast MX where you want a broad power band with great horsepower in the mid range. The PC pipe had a narrower power band with more of a hit in the upper mid range.

I hope this is helpful.

The bike works great now!:cool: