Latest tuning info on 04rm125

[bclapham]

You Brits are a hard headed lot! :)

and we take crap from no one either! :p

i agree about the mains, but the point i raised simply re-iterates what i have been saying all along. apples and oranges- that OEM TMX carb with the reverse cresent is so much different from the other carbs, the needles wont interchange between them either since i looked into it. then figure different airspace between the slide and reeds, different float bowl etc etc etc, it becomes very evident to me that you cant compare main jets from carb to carb.

 

[steve125]

Certainly not exactly the same in performance youre right. But when at full throttle, the slide matters little at that point, as does the needle. So whats left? the pilot size and the main jet and the true bore of the carb. I feel they should be close at WFO with the same mains installed, as long as the mains are smaller than the nozzle. In this case Mikuni would not make a main jet larger than the nozzle diameter, that would be counter productive.

And Marcus i hope you see the light that nozzles don't affect the mains or vise-versa :moon:

 

[bclapham]

the true bore of the carb.

steve, the world exists in three dimensions, and the bore of the carb is only two! i think the area of space between the main jet and the reeds has a lot more to do with it than the area at the back of the carb! Just my opinion! :thumb:

 

[marcusgunby]

Well i look at things from a different perspective on this, i dont really care either way(LOL) but if what you say is true all 125s with the same carb would run the same main-this is clearly not the case so the evidence says to jet for the bike and the locallity.
Im with bruce in the fact that some needles seem to need different mains, the ktms guys have found this by running too lean when just swapping a needle.

If you really want to look closely as the systems try to imaging the fuel passing past the main jet hole then the needle taper and then the nozzle-you cant tell me the flow will be totally uniform in this area with all the steps etc, and this may have a bearing on how big the main needs to be, in a perfect world your idea maybe spot on, but in this side of the planet its a case of lets not blow a good motor because a guy in the states runs different jetting.

If i am running very rich jetting i have a even better motor than i thought.

 

[steve125]

LOL Bruce! I think a step in main jet size would matter more than just a few mm's in the difference from the fuel delivery location in the carby throat at 11k RPM. If both carbs are real close to a 36mm bore then at WFO throw the slides out the window and the needles. It's all about the mains there matey :thumb:

 

[bclapham]

no steve, thats not what i said- the area between the jet to the reed is different from carb to carb type- wouldnt you expect this to give a different signal at the jet?

 

[steve125]

Marcus the difference has to be in the fuel! My bikes will not run on your jetting nor yours with mine. So just what is the difference? Porting? pipe? ign? nope that stuff is all so close to the same.

I just don't understand if it's possible? to run a needle with a tip so fat it restricts the main jet flow at WFO. Speaking of inconsistancys that set-up would be just plain stupid.

 

[steve125]

no steve, thats not what i said- the area between the jet to the reed is different from carb to carb type- wouldnt you expect this to give a different signal at the jet?

Why would the area be different if both carb bores measure at 36mm and the nozzle distance to the reed tips are real close to the same?

 

[bclapham]

nozzle distance to the reed tips are real close to the same?

i dont know that the distance is that close, is it? i know my PWK is around 15mm longer than the OEM TMX at the front- thats why i made it shorter.

 

[steve125]

The Keihin's have a much longer carb body than the Mikuni's. The 2 Mikuni's we have been talking about I feel are very close.

 

[bclapham]

dont forget that the 04RM motor has the longer rod- doesnt that weaken the signal and hense need richer jets?

 

[DEANSFASTWAY]

Maybe on a mod motor with lower CCR with like a spacer plate maybe . On the RM did they make the cyl taller or just move the pin bore ?

 

[bclapham]

Dean, they made the cylinder taller- On Erics site, he now has the retro kit with the spacer plate.

btw- what effect will lowering the crankcase comp ratio have on performance- i suppose you can reverse this with epoxy???

 

[DEX]

I am currently racing a 01 KX 85.
But have been seriously looking into the 125 class and have pretty much decided on the RM 125....(2nd choice the CRF 250)
I was wondering what mods other than the crab were done to that bike in the graph? What change gave the RM the crazy dead spot which I would think would have some effect on coming out of turns and starts unless you kept it pinned.??? Im not sure... first year racing would it not matter cause you drive on the bike anyways and not done at that low rpm even when going slow cause you got it reved up with the clutch in slightly....(hope I am making sense)
What kind of money would these mods and what ones would make a big difference yet not involve alot of internal work?
I am guessing you guys expermented with alot of the different bolt on mods also?

 

[marcusgunby]

DEX the low rev glitch was just a jetting problem i have sorted with a richer clip poition and pilot-the carb was like on a 2001 Cr250 but it was bored to 39mm.On the track theres no dead spot really, the major changed needed on the 2004 rm 125 are

1)pipe-lots to be gained-dont get a HGS however.
2)PV mods-the pv has to be modded when you hop up the engine-the timingof the pv is all wrong.
3)big carb-it really likes them.
after that you can look into porting and head mods.

Im going to try a boyesen 3 rad valve next but i dont expect to see a big gain.
I dont really like v forces much these days as they seem to make the bike have a hole in the power down low.

Do a search for tuning rm125 and you should find my older threads from the start of the year.

 

[bclapham]

Dex, i know a couple of kids that have come up to the 04rm125 from 80s- the good news is that compared to the other bikes in the class its quite plush suspension wise, but if you are less than 130-140lbs you might need lighter springs.

as for the engine, the ones i saw ran really rich so try and understand how your jetting works, that will help a lot for a crisp running engine.

dont think its a bad bike without all the above mods, its a great bike- ole Marcus here is a wiley old vet that wants every last ounce of power from his bike so he can stand up and fight against all the 250F cheater bikes!!:):)

 

[marcusgunby]

LOL bruce i have no fear of the 250f ,its the modded 250 2 strokes and 450fs that im struggling with:(

 

[250racing]

marcus what do you think i could do to my 04 rm 125 to get better low and mid power? i dont mind sacrificing a little on top since i ride enduros. my bike is bone stock and i have only ridden it for 1 hr. since i got a left over bike last saturday.

my only other 125 i had was a 99 cr and the suzuki eats the honda alive.