04 RM125 tuning info

[steve125]

Marcus the only thing I can't figure is how you lost some over rev with a timing retard and head mod on your best run??

I suspect the head mod, what was done? You may need to lower the MSV. :think:

 

 

[elf]

That orange line sure looks good on that 03 dyno! heh hee.

 

[marcusgunby]

Steve i adgree totally, i think the peak went up and the overrev went out the window-i will try to mod bruces old head to the std specs.

 

[steve125]

Hummm??? maybe leave the head alone and raise the exhaust a "bit"?

Have karl shorten the head-pipe 5mm and cut you a few spacers to shim it back out if needed? Remember how that has helped out on some of my motors when looking for over-rev.?

A bit leaner on the main jet?

You are sure you have retarded the timing??? Clockwise advanced right!!??

I think I would raise the exhaust .5 and then tune with timing and exhaust length. The head mod you have done should work well along with raising the ex-port.

If you want to go farther with the ex-port, it would be a good idea to follow Erics advice and raise the ft. transfers to 1.0mm also.

 

 

 

 

[elf]

In your quest for every last bit of power have you guys ever tested different types/weights of trans oil? I made sort of a lame search for this but came up with nothing.Was just wondering if thinner oil in trans would show up on the dyno.

 

[marcusgunby]

Anything that creates less drag will appear to show more power as its a inertia dyno.You can do a few things to make higher numbers, thats why you cant trust the mags always.

 

[elf]

I see. And I thought I could trust the mags.lol

 

[147leeman]

Steve125 and marcusgunby,

I've got an 02 RM125 with a motor done by PR2 (actually it's my nephews but I can race it since I bought it). Looking for better torque and more horsepower everywhere as I weigh 170 lbs. and also race a CRF450. Do you guys have any dyno curves for a stock bike of this year? I know 04 changed many things in the motor department, but I'm thinking of either a 133cc kit done by eric or a 2mm overbore + 2mm stroker to keep the revs up. Steve, I've noticed you've done a few 144's, but I'm worried about ring wear as I ride in the upper end of the power curve all the time, also I noticed your dyno curves of the yz144 kept it's power through the rpm's...what port job did you have to mimic this?

So far I've jetted it clean for MR2 and the bike was purchased used with the PR2 work and FMF pipe/shorty silencer done to it previously. I just need more torque and horsepower to carry me around faster! Any help with this model year would greatly be appreciated!

 

[marcusgunby]

Ive seen the dyno for the 03 and it wasnt pretty, the 03 and 02 i suspect, will never go like a 04 can due to the design of the engine.The works 02s,03s had the long rod like a 04.I would go big bore and get a good pipe.Reeds and carbs on at least the 03/04 was good.

bruce know more the changes from 02 etc as i have only been a rm fan since the new engine.

 

[dbrace]

Marcus,
I was just wondering, you said the iCAT did nothing for you. Was this just from the dyno result or track testing? The Yamaha team here in Australia also dyno tested them and weren't too excited but when they track tested them they said YES. They are now using them for the 2004 sx/mx series!

 

[marcusgunby]

I never rode it, our weather is very wet at present, i think it helps clear up low speed jetting.I would be happy with that and no power gain if the price was better-i was thinking of its worth about £50 or $75 not the three times that amount they charge.

 

[georgieboy]

Bad weather here also, but i managed to trailride yesterday(only dry day in a week) next weekend looks better though.
Marcus and Steve, will you two be so kind to explain some more on the differences between the cilinders, 2002/2003 compared to 2004.
Why a cilinder is better in general and what you guys do to figure that out.
I don't want secret porting maps or degrees just general stuff.
Maybe it can't be explained but if you can pls. thx
It is bad weather here so i might as well learn some more.

 

[Pete Payne]

Originally posted by marcusgunby
:worship:

Was that the HDR KX 144 ????

 

[marcusgunby]

LOL pete-it wasnt a good engine as it was too fast:)

 

[steve125]

LOL! Marcus was so funny Pete. When I asked him at the end of the day how was the KX144. He rolled his eyes and in that Brit accent said, "I can't keep that damn front end down long enough to make the next corner" :)

 

[marcusgunby]

steve do you want to answer georgia boys question as i feel you have a better knowledge of these matters.

 

[bclapham]

what bike are we talking about?

ps. ive got a brand new fatty pipe for a rm125 with 2 races on it and its well duffed up- i thought when i crashed it was just dinged up but its pushed in/bent to the point where it has squashed the coolant hose

anyone knowa easy way to straighten them out???

 

[steve125]

Ok! But I'm not to happy with Honda right now with the 450 being such a great bike and the 2 strokes are still slow :|

I read a few tests on the 04 CR125 and they say it is still slow. I haven't ridden one and really don't want to, I'm sure it's slow.

I haven't seen a 04 cylinder so i won't comment.

The 02 and 03 cylinders are completly different and won't interchange on either models. The 02 has the best spec of the 2, the 03 is too advanced in its port timing and transfer window area. Honda put a large reed block in for 03 and then mounted a huge reed stuffer that, well, took away all the advantage of the large reed block :think: Thats a good thing due to the fact they went to a large 38mm carby and the port timing being so advanced, brought back some lost response.

Truly a cat chaseing it's tail at this point the 03 motor. Advanced port timing for top end. 38mm carby for more mid to top. Big reed block for top end and for show but because it so restricted with it's oversize stuffer. They might as well left it alone. Cylinder head designed for low to mid power. Pipe designed for mid power with a large core silencer designed for top power.

All this had the motor working against its self. Very poor way to tune a motor and no wonder it's slow.

So GB we don't just look at say the cylinder and judge a motor. Like the KX144 and the YZ144 or Marcus's RM125. You just don't get that kind of power, unless all the components are in time with each other. Thats the goal and only testing will get you there.

The 03 CR 125 is a text book way in how tune for a slow 125 engine. Kawasaki copied the YZ 125 and Suzuki did the same with KTM125. I think Honda has out smarted itself, refuseing not to learn from the competition. Too bad because they have one of the best chassis.

 

 

[marcusgunby]

Great info steve but i think georgia boy was talking the 04 rm 125 and i was hoping you could tell him why a long rod and flat top piston work so well with a no bridge ex port:) ;)

 

[steve125]

Originally posted by marcusgunby
Great info steve but i think georgia boy was talking the 04 rm 125 and i was hoping you could tell him why a long rod and flat top piston work so well with a no bridge ex port:) ;)

Cuz KTM says so!! :worship: :yeehaw: :)

 

[georgieboy]

Yes that is what i mend but great info nevertheless. I like it when poeple who know what they are talking about aren't shy with words.
Makes you wonder what the manufactures are thinking about when they create a package called motocrossbike. They just flip things together accidently or is it their goal to create an aftermarket?
So that the smartest guys have the fastest bikes?

 

[marcusgunby]

I will try to help with more info as steve is playing the comedian:)

The long rod is a good thing as it has a longer dwell time at Top dead centre, this is better(rich may tell you why) also the leverage(maybe not leverage , mechanical advantage) the rod has on the crank is more at half way through the stroke, giving more torque,the bridgeless exhaust port allows a greater port area without risking extreme ring wear.Not sure why all companies dont do the same.The Husky cr125 has 3 transfers(each side) for greater area and less wear.Small ports giving faster flow but the same total area.

Flat top piston isnt easy but its lighter and seems to work well in mx-i think road race like the dome pistons.

Any way erics site has a write up on flat top vs dome pistons.

Does that help?

 

[bclapham]

Originally posted by marcusgunby
I will try to help with more info as steve is playing the comedian:)

yeah, but it wasnt that funny! :laugh:

 

[georgieboy]

tsjees i didn't understand why he was discussing a cr cilinder when the topic was about rm. But the thing with me is i am happy with any info even when it is offtopic i guess.
So thx Steve, and you too Marcus for helping Steve lol.
I assume these rm cilinders have a main exhaust and two sub exhaust ports?
Are there any pics available maybe?

 

[147leeman]

Would taking my 02 RM125 and getting a 2mm stroker kit bring it closer to the 04 RM's specs? My options right now are:
1. getting the 133cc
2. getting the 2mm stroker kit
3. getting teh 133cc + 2mm stroker

What are the drawbacks of these options?
Marcus, thanks for the info on the difference between the 04 and 02/03 RM engines.