Can I De-Tune my 03 RM250?

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#1
Hey there,
I have a power problem...too much, well actually the overall power is nice but the midrange is just too brutal for tight woods. I up-shift to tone it down and the low end gets unacceptable real fast.

I run the Steahly 10 oz weight with an FMF Gnarly pipe and Q muffler. The bike is set up for woods but the motor still feels like its wants an MX course which it never sees.
My thought is to try the stock pipe which never seen use yet to tone down the midrange but I don't want to loose any low end.

For smoother power delivery can I change something else like a thicker head gasket or change timing?
I need smoother power off the bottom for rock crawling and such.
 
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#2
I was in the same boat when I moved from SoCa and began riding trails of the central coast; wanted something more manageable at lower RPMs as desert riding was a thing of the past, and slower, tighter conditions prevail here. Eric Gorr had previously mildly modded my stock cylinder + head for more power everwhere, and it worked very well for the desert and other go-fast conditions. Therefore I bought an extra cylinder and had him port it for low to mid.

I believe his excellent book says (effectively, in this order) lowering the transfer ports, reshaping the head's dome, and perhaps increasing compression will accomplish what you are looking for. (Rich R. will post exactly what the book states any mninute now, to follow!)

If it had a tachometer I could be more specific but what his porting did was shift the plateau and "ramp up" to the left, peaking at lower RPM. I'm very pleased with the outcome. Well worth the $ - he knows his stuff.

At elevated RPMs it still has more than needed so I'm wondering if a Dynoport pipe and S/A would help shift even more to the left; am musing if someone can confirm their claim - althought I have no reason to doubt, it would make it easier to sell the idea to my wife (gee: what's this shiney new part cost that just came in the mail? Is it really neceessary?)
 

Erick82

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#3
Stock pipe will make the mid hit stronger, try some v-force reeds, if it dosen't change it enough, then go for the porting.
 
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#6
Originally posted by fuzzy
Need a wide ratio trans :)  ala RMX
Don't laugh: the RM and DRZ gears can be interchanged, according to the Zook off-road team; two of the Yosh DRZs had an RM trans.
 

fuzzy

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#7
Sweet! There is your solution my friend...You can bet your butt that Team Suzuki's GNCC bikes have this setup! Same w/ team yamaha's YZ250's having WR gears...
 
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#8
Originally posted by fuzzy
Sweet! There is your solution my friend...You can bet your butt that Team Suzuki's GNCC bikes have this setup! Same w/ team yamaha's YZ250's having WR gears...
Well, the Cycle News article mentioned the WORCS DRZs, not the GNCC RMs. Nonehtless you have the right idea.
 
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#9
Thanks everyone for the advise, I may try the DRZ gears but as I spend more and more on the bike to get it to fit and feel like my old EXC I have to stop and ask - why should I keep changing and modifying this track bike to work like something its not intended for? Still it is fun to show up at the events with something other than orange, dang those bikes have taken Enduro's over!
 
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#10
EruoDude,

Try increasing the preload on your exaust valve spring. If you put more preload on the spring, the exhaust valves will open later (at higher rpm's). Keeping the exhaust valves closed longer (for more of the rpm range) should give you more usable torque and less of a hit.

This won't replace a porting job, but should give the bike more low end torque for more of the rpm range. Plus it's a free mod.

Hope this helps, Steve.
 
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#11
what if you go down one tooth on rear sprocket so you wont have to shift up to tame the power, and go to a 16 oz flywheel weight? if you put a small dent on the underside of your pipe, next to where your cylinder almost touches your pipe, that will mellow it out,, at least it did on my yz.
 
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#12
EuroDude,

I forgot to add, try a smaller front sproket. Go down a tooth or two. This will mimick a larger rear sprocket for about 1/3 of the cost. It's another inexpensive way to change the gearing.

Although this will make the bike "rev" quicker (higher numerical final gear). You will be able to handle those tight sections at a more controled speed using the same gear in the same rpm range as before.

Steve
 
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#13
Originally posted by snb73
EruoDude,

Try increasing the preload on your exaust valve spring. If you put more preload on the spring, the exhaust valves will open later (at higher rpm's). Keeping the exhaust valves closed longer (for more of the rpm range) should give you more usable torque and less of a hit.

This won't replace a porting job, but should give the bike more low end torque for more of the rpm range. Plus it's a free mod.

Hope this helps, Steve.
Hey Steve,
I see 4 springs in te Exhaust valve assembly, looks like the exhaust valve return spring can be preloaded with addition turns on the cap that holds it in. There is also a spring on the exhaust valve Governer that would require shims to preload it. Are you talking about the first or second one mentioned?
 
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#14
EuroDude,

I'm refering to the spring that is located on the top left side of the cylinder(#14). You should be able to loosen the two screws(#13) holding the exhaust valve retainner(#12). Turning the exhaust valve cap(#10) clockwise will increase the preload. I wouldn't mess with any internal componants.

Here's a diagram, yours should look simular.

http://houseofmotorcycles.bikebandit.com/partsbandit/showschematic.asp?dept_id=124027

Steve
 
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#15
Originally posted by snb73
EuroDude,

I'm refering to the spring that is located on the top left side of the cylinder
Here's a diagram, yours should look simular.

http://houseofmotorcycles.bikebandit.com/partsbandit/showschematic.asp?dept_id=124027

Steve
Cool, thanks Steve- that is the one I was thinking about. Factory setting is 1/2 turn preload. I will try 1/4 turn at a time past and test it out.