Jump to content
Sign in to follow this  

RM 125 jetting help

Recommended Posts

Hi folks i posted a similar thread in the jetting section but not one single person had an imput so maybe you can help.

I have a 2003 RM 125. In the carb it had a : 560 main, 40 pilot and needle on the 3rd clip.

In my manual it said stock was : 460 main, 42.5 pilot and needle on the 4th clip.

So i dropped the main down to a 460 but it didn't make a massive amount of difference. I checked out the parts diagram on here and there was two sizes for the main jet, 19.1 and 19.2 which were 460 and 560!

It is still running too rich after apparently dropping 10 sizes on the main. So I'm well confused now and not sure how to make the jetting better.

I run motul 800 at 32:1 and it has a DEP silencer. 

Thanks

Share this post


Link to post
Share on other sites

At what point is it running rich?  And are you counting needle positions from the top down or bottom up?  Also, what about the air screw setting and the choke height setting?

 

One fool proof method that I've found with jetting is to just buy a JD jet kit, their not cheap but they work great!

Share this post


Link to post
Share on other sites

Im counting needle clips from the top so its here

-

-

-

x

-

Seems to be rich all the way through but more so in the first part of the throttle. 

Choke height settings? Do you mean the float height? That is within manual spec.

I don't understand how dropping 10 sizes in the main didn't make a huge difference. In the thumper talk parts fiche it lists two main jet sizes.. the 460 and 560.. 

Thanks for your help.

Air screw is set around 2 screws out. 

I just ordered a carb kit from America so hopefully that will help out.

Edited by owainyz03

Share this post


Link to post
Share on other sites

You are on the needle 75% of the time unless it's serious mx racing you're doing. Put that clip in 2nd from the top and go with stock setting on the main and you should be way better.

Share this post


Link to post
Share on other sites

Okay I'll give that a try :thumbsup:  I'm not WFO all of the time. I'll test that out as soon as I can and report back.

I haven't swapped out the pilot yet I might try a size down if the new stock size doesn't improve. 

Thanks for your help!

Share this post


Link to post
Share on other sites

So my carb kit arrived today from the US. Included all o rings, main jet,pilot jet, two float valves, needle+clip, air screw and idle screw

20140820_132251.jpg

20140820_154006.jpg20140820_153229.jpg

Sorry for the phone pics. Installed a 460 main, 40 pilot and needle on the middle clip. I am heading to the track on sunday but might try get a ride in first

Also this is the plugs I'm using

20140820_180544.jpg20140820_180339.jpg

Share this post


Link to post
Share on other sites

On my 02 I ran a 430-440 main. 27.5 pilot jet. Middle clip, air screw 1.5 out. And then mess with idle screw to desired. My bike was crisp and would idle for days. I ran yamalube 32:1. I also had a fmf sst pipe with a shorty

Share this post


Link to post
Share on other sites

On my 02 I ran a 430-440 main. 27.5 pilot jet. Middle clip, air screw 1.5 out. And then mess with idle screw to desired. My bike was crisp and would idle for days. I ran yamalube 32:1. I also had a fmf sst pipe with a shorty

27.5 pilot? wow thats a big difference! Track cancelled practice so it won't be till next weekend i can ride

Share this post


Link to post
Share on other sites

I recommend going to the 27.5 and going from there. At one point I had a 25 with a 420 but that was a little on the lean side

Share this post


Link to post
Share on other sites

try what goozey46 is running.  be careful with the main jet though. 

 

I rebuilt my 2002 rm125 in the fall of 2012.  it was a non running project bike.  my altitude is 900 feet.  I used a JD jetting kit with a FMF fatty pipe/ shorty silencer.  13/52 gearing and engine is otherwise stock. 

 

I used the 27.5 pilot as instructed, but never got down to the 430 main jet as instructed.  I use a 450 main, and my plugs are just right.  I did install an aftermarket air/fuel mixture screw and I adjust it on each ride after warming up the motor.  this seems to help tremendously with throttle response and idle quality. 

 

there is a company in the states called RB designs.  www.rb-designs.com   I had him set my squish on my head  and do his carb mods on my 2004 gasgas ec300 and it made a night and day difference.  currently he has the carb off of my 2007 ktm sx 125. 

 

also, do a compression check and bleed down test on your bike to see if the crank seals are good.  bad crank seal will suck air and cause nightmares while jetting.   

 

I will be glad to go to my shop and dig out my jd jetting kit and tell you what I used for sure if needed.

Share this post


Link to post
Share on other sites

also you need to consider running a NGK R6918B-8 spark plug in your rm125.  this is the oem spec plug and will safeguard your engine from the ground strap failure with other spark plugs. 

 

some folks have lost an engine due to the ground strap vibrating loose while the engine is running.   

Share this post


Link to post
Share on other sites

@Lindsey97 I considered that plug until I saw the price tag :jawdrop:  :jawdrop:  So I went with the erudiums 

I guess I will drop the pilot down to that, considering there is a 40 in it. 

Compression is good as the bike was rebuilt only a few hours ago. I haven't noticed any symptoms of airleaks but i will check.

The jetting isn't awful but I would like it to be better 

Thanks for your help :thumbsup:

Edit I wish i could get jets as cheap as you US guys. Im gunna pay €12 (15$) for this one jet....

well let's hope it'll help!

Edited by owainyz03

Share this post


Link to post
Share on other sites

Just brand new stock jets. 460 main 40 pilot (have a 25 also might try that next time) needle in the (middle)3rd clip i think and air screw about 2 turns. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...