Jump to content

Smoothing out a 125 2 stroke

Recommended Posts

I recently picked up a 2001 RM125 for a decent price for something to play around with.  Ever since I bought my new Husqvarna TE250 I've been missing having older used bikes to fix up and tinker with.  It runs and rides good as it is now, but I want to smooth out the 125 powerband hit for trail riding.  No fun trying to set up a log jump or get a little air off the top of a hill and have the powerband flick up on you.

When I was thinking about getting an 85 for my son, a local guy who has been riding for many years, told me I could try putting a washer where the pipe mates to the cylinder as that is what he did it to his sons Yamaha 85 when he was learning.  I haven't done it to my sons KX85 as I don't think it needs it.  It already has a pretty smooth transition.

Remembering this I thought I would try it on my newly acquired RM 125.  I looked through my parts bin and found a washer with the perfect outside diameter (OD) to fit in the pipe.  The inside diameter (ID) was small (it wouldn't fit all the way on my pinky finger) but I had it so I was going to try it.

Popped it in and went for a test spin.  The difference was awesome!  The ole' RM125 now sounded somewhat like a KTM Freeride!  It had more bottom end and the transition into midrange was super smooth, but it had zero topend.  So I felt this had some potential.  I went to Menard's and bought some different size washers to play with.

The next one I tried (and is still in the bike) had a larger OD and ID.  So it is not in the pipe but is sandwiched between the pipe and the cylinder.  Now it still has improved bottom end, a smooth transition, but now the top end is better.  I have only test ridden it in a field but plan to hit the trails with it today for a real world test.   Before I didn't feel comfortable riding standing up and trying to power up a wheelie like you would do for a log crossing because it didn't have enough meat to get it up, but once it did you better be quick.  Now I can give it throttle and pull up and it will come up smooth similar to me TE250.

I think next I'm going to dremel out the ID of the hole 1/16" -1/8" to get back more top end yet still keep the smooth transition.  This is a fun bike to play with!

I'll try posting pics from my phone...

  • Like 1

Share this post


Link to post
Share on other sites

Out of curiosity what size washer ( Id and od) have you ended up with?

Share this post


Link to post
Share on other sites

I'm using the one on the right, not sure of measurements.  Runs great IMHO, but I think I'm going to dremel the hole out another 1/8".  That should help get her a little more umph put still keep it smooth.

 

Edited by Yokomo
  • Like 1

Share this post


Link to post
Share on other sites
1 hour ago, Yokomo said:

I can't measure the larger one since it's in the bike.  I just measured the 2nd from the right and it is almost 1 1/2" OD   3/4" ID.

Did you grind down the bigger washers OD to fit in the pipe , if you had to guess the ID of the bigger washer would you say 7/8" or 1" ?

Share this post


Link to post
Share on other sites

The next one I tried (and is still in the bike) had a larger OD and ID.  So it is not in the pipe but is sandwiched between the pipe and the cylinder.  Now it still has improved bottom end, a smooth transition, but now the top end is better. 

Actually the ID of the larger washer is a little bit smaller than the one I measured.  Doesn't look like that in the pic but it is.

Share this post


Link to post
Share on other sites
9 hours ago, Yokomo said:

 

Actually the ID of the larger washer is a little bit smaller than the one I measured.  Doesn't look like that in the pic but it is.

18mm ?

  • Like 1

Share this post


Link to post
Share on other sites

Memory failed me. The larger washer I have in it has a larger ID diameter as well.  It is 7/8".  I just now dremeled it out larger.  Now it is about 1 & 1/16".  The OD diameter of the larger washer is 1 3/4".

Time for a test spin...

Took it for a quik spin.  It still has a pretty smooth transition, but now it has a little more bark when the reeds open.  I would equate it to running a yellow spring in a KTM, and then opening up the dolly screw 1/2-3/4 turn.  I'm liking it!

Edited by Yokomo
  • Like 1

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:


×