FMF pipe

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gregp
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FMF pipe

Post by gregp »

I finally scored a used FMF Woods pipe. A local was nice enough to sell it to me for $30, with a great molded plastic pipe guard! The pipe has a golf ball sized dent in the fat portion of the pipe, but it does not seem to affect performance much at all (I had a *perfect* woods pipe on my '96 - so I know how it should feel). Now, with the pipe and the V-Force cage, the motor absolutely rips compared to stock. I may experiment with a weaker spring in the power valve detent assembly, though, as I want to get the valve to open a bit sooner. I have taken the ball and spring completely out, but the bike gets a bit violent when they are removed.
Maybe I could replace the balls in the PV governer with heavier carbide balls... but a weaker spring seems like an easier approach.
I am going to need Gold Valves in both ends next...
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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Post by fuzzy »

Interesting prospect....Never seen anyone mess with the centrifugal engagement. Changing springs and/or weights(balls) is of course common in other centrifugal applications. If you can find heavier balls that's probably easiest.
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Post by gregp »

I removed the spring and detent ball again last night, and took it for another ride. With the pipe (and the reed cage) the motor behaves much differently, in a good way! It has much more low end now (than with the detent parts removed and with the stock pipe), and I am very happy with it. There is plenty of low end, and the bike comes on the pipe much quicker.
I will leave it like this until I can get a good, long trail ride in and see how much I like it once I get tired...
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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rbates9
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Post by rbates9 »

>|<>QBB<
gregp wrote:I removed the spring and detent ball again last night, and took it for another ride. With the pipe (and the reed cage) the motor behaves much differently, in a good way! It has much more low end now (than with the detent parts removed and with the stock pipe), and I am very happy with it. There is plenty of low end, and the bike comes on the pipe much quicker.
I will leave it like this until I can get a good, long trail ride in and see how much I like it once I get tired...
What keeps the PV from just floating with no spring? I was just thinking about a different spring tonight due to my friends KTM with interchangable springs. I would like to know more!
gregp
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Post by gregp »

The detent spring assembly on these motors does not "pre-load" the power valve to the closed position like the KTM assemblies. On the KDX motor, the detent assembly merely "locks" the valve closed until sufficient force is generated from the governer assembly to overcome the detent. By removing the spring and ball in the detent assembly, the power valve is still regulated by the governer, but it opens much sooner.
The detent assembly is located on the left side of the motor, right under the round, slotted cover, up by the exhaust port. Directly beneath the cover is an 8mm hex head bolt with two copper washers under the head. Remove this bolt - but be careful! The bolt is hollow, and it has a small spring sitting inside of it, with a small ball sitting right on top of the spring. Simply remove the ball and spring, and put the bolt and washers back in.
The whole process takes about a minute to do, or undo, and it has a big effect of the motors behavior.
Go ahead and try it. If you do not like it, you can return the assembly to its stock configuration in a minute or so. You will definately feel the difference.
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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Post by gregp »

I recall somewhere that Jeff Fredette was asked about this modification, and Jeff replied something like "Yea, you can leave that out if you want to".
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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Post by gregp »

My seat of the pants guess is that in stock form, the valve probably opens at 5-6000 RPM. With the ball and spring removed, it probably opens at 3-4000, which is a huge difference.
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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Post by SS109 »

So Greg, are you still happy with the governor mod or did you switch back to stock?
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Post by gregp »

I ran the bike all last Fall without the spring and ball, and I liked it. When things started to get icy and snow began to fall, I put the ball and spring back in for better low end throttle control. Overall, This "mod" is quick and easy, and makes a significant diiference in power delivery. For super-tight, trials-like conditions, I am better off to leave it stock, but if the riding is more open, and fast, I like it out.
I never ended up getting heavier balls for the governer, as they were not needed with this modification.
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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Post by ecojbr »

You guys have my curiosity, so I removed mine and guess what, the previous owner had already removed the ball and spring. And I was hoping for a hop up. Really don't wanna put one in, afraid I wont like it
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Post by rbates9 »

I have not tried removing the ball and spring but it may be worth trying it with the ball and spring installed just so you know what the difference is. I forgot about this over the winter and will probably try it tomorrow.
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Post by gregp »

My bike has 2 small copper washers under the bolt head. I would guess that if you removed one of the washers, the power valve would be held in the closed position a bit longer.
I have found this mod to be a quick and neat way to play with the power valve adjustment. KTM's have different springs that you can install to get a similar effect.
I do and undo this relatively frequently, depending on conditions, and what kind of ride I am expecting to go on.
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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Post by gregp »

>|<>QBB<
ecojbr wrote:You guys have my curiosity, so I removed mine and guess what, the previous owner had already removed the ball and spring. And I was hoping for a hop up. Really don't wanna put one in, afraid I wont like it
Putting these pieces back in will give you better low end, and a longer, smoother transition to the top end power - good for sloppy conditions! Not so much for wide open stuff.
2004 Dual Sported KDX200
1999 Ninja 250 (Daughter's)
1996 DR 650 (stock, mostly street use)
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Post by ecojbr »

How much "real" difference is there between the two?
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Post by fuzzy »

It's a preference on delivery thing. Strap the bike to a dyno and you won't really see it....Other than a shift in the RPM point where the PV opens to increase peak power.
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
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Post by ecojbr »

As soon as the rains quit(if they ever do) I am gonna try it both ways. Coming off a 125 into my hybrid I am sure I wont like but I will give it a try. One never knows until it is tried!!!!!
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Post by rbates9 »

I just tried removing the spring and ball on mine and it makes a very noticeable difference.

First I rode the bike around on the driveway and a small loop in the woods that has some straight aways and some pretty tight weaving thru trees type of first gear kind of stuff.

Then I removed the ball and spring and rode the same loop and on the more open stuff it made the bike feel a lot quicker (like has been said) but once in the tighter stuff it just seemed to want to spin the back tire instead of lug. Over all it is a good thing to know and I will probably try it again in the future but I don't think it's for me in most cases.

Thanks for the tip gregp! Any thing free that actually makes a difference is good to know.

P.S. it only takes less than a minute but that pipe is VERY hot during that minute. :shock:
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