03 RM125 Torque/Bottom End Mods

[Chili]

I am going to be tuning one and assisting in tuning another 03 RM125 this coming season. Both riders are advancing from 80's into their first season of 125B. I am not trying to turn these bikes into absolute horsepower monsters as I think they will have more power than either of these riders can use for this season. I just want to give the bikes more bottom end to help these two racers as the 03's were supposed to be a little more difficult to keep in the power.

First mod will be going up a couple of teeth on the rear sprocket. From there I am not really sure what other mods will give me more bottom end/torque. A reed spacer between the reed block and the cylinder was recommended by one tuner, not sure if this has any effect or not. Any other mods besides the obvious porting change that will give us more torque/bottom end?

 

[flyinzuki]

Cometic high performance top end gasket kit has a thinner base gasket
Try some VP ultimate 2
I don't think FMF makes gnarly pipes for 125's
Dyno port might make a torque pipe, "big volume"
Try adding spacers to the pipe, between cyl and pipe
Shorten the silencer
Torque reeds
Reed block spacer "should" help

 

[KX02]

No fmf does not make a gnarly for 125's. After upping the rear sprocket you might try differents reeds or a complete V force set up

 

[bclapham]

Chilli- what you are wanting, is like asking a beautiful brunette to bleach her hair blonde!:)

for the sprokets, dont go too mad- ive tried it and it can make the bike real gutless- it just goes nowhere fast with the big back sproket.

as for v-force, steer clear the low end jetting will be so off you arsking for trouble. i am not sure reeds and spacers will help much- the stock settup and carb sounds good- Dean, Steve????

do you have good fuel? the stock base gasket is 0.5mm thick- you can run the cometic high comp kit- here the base is 0.3mm dropping the ports a bit and the extra comp should bump the low end throttle response a bit.

as for pipes, my 144 is on stock port timing so it should be similar, the fatty has more bottom than stock, but falls off a lot quicker than the stock on top. you can even add a few spacers to the front section of the pipe like ochster did on the SX bike- you know the little washer- 2-4 should help. you could also shorten the silencer a tad or even the fmf shorty, marcus D'ned the pipes so we will wait for his comments.

does the 03 have that PV adjuster spring??? i think messing with that can be trouble if you dont have a dyno though.

at the end of the day, i wouldnt go too far looking for low end since you will lose the best part of the motor- keep nagging the lads about that clutch, if they are racing i am sure they will get fed up with getting left in the corners and start using it- in 6 months you see him jerking the bike through the pits, you know its time for a billet basket and your work is done! :worship:

 

[marcusgunby]

The bills pipe is good for the rms, dont think much to the v force-going to test a boyesen 3 rad valve soon on the 04-be careful increasing compression on the 03 as its high already, good jetting as the 03 comes very rich.

try backing out the pv adjuster half a turn and see if it pulls better-they appear to be too tight from new.

 

[Chili]

I already have a complete FMF SST setup that I picked up real cheap. I hadn't decided whether to leave the stocker on and keep the FMF for an emergency or not. I imagine LazyBoy will want the "shiny" pipe :laugh:

After reading many threads I will not touch a V-Force and will probably just stay stock with some sort of carbon reeds desinged for low end. Anyone have any experience or thoughts on the reed spacer? I am trying to avoid dropping big dollars as this will most likely be a 1 season bike before we go to the dark side. :think:

Bruce as for fuel that is another jackpot that I haven't made a decision on. VP C-12 was about $80 CDN for a 5 gallon can here last season. LazyBoy tends to go through about 15+ gallons a month. Calculating the difference between premium pump and C-12 will add approx another $1000 + to the race budget that I'm already struggling to maintain. I know the benefits of the fuel are great but at some point we need to draw a line.

 

[bclapham]

try backing out the pv adjuster half a turn and see if it pulls better-they appear to be too tight from new.

thats quite a lot actually mate- the PV spring has about half a turn of preload as stock- i think this setup needs only small adjustments- Deanfasty knows a bit more i think and i bet he knows about them reed spacers, Dean??????

Chilli:

i understand on the fuel, believe me i do! when i was a pro-practice rider, i ran straight C12- now i am racing, i have to mix it 50:50- ironic really!

on the next topend, take some measurements on the squish etc and see where we are- a small head mod along with that thinner gasket could help a bit.

talking of RMs, Travis just posted 3rd fastest time in practise at Daytona! :yeehaw:

 

[marcusgunby]

bruce half a turn-well thats very different to the 250 guess i need to not assume so much? well then i would say only a eigth of a tun less then? you can always go back to std.

On the reed spacer-some bikes like it-it will make getting the carb back on hard and the boot may rub on the shock spring.

The 04 cr250 benifits from a huge reed spacer-something like 10mm. However it doesnt like the exhaust spacer(manifold) from the 03 cr250-you have to just try these things really.

 

[bclapham]

its all coming back to be now- marcus makes good points, there is a bit of room though- my carb is about 12-15mm longer than stock and it just touches the spring, so with a 10mm spacer you should be OK.

now, as for the spacer, thats easy- the RM uses the same manifold bolt pattern as the yz125. there is a guy selling the reed spacers for the yz cheap on ebay