'03 RM125 starts and stalls over and over!!

Discussion in '2-Stroke Discussion' started by bigboss_an, Feb 20, 2012.



  1. bigboss_an

    bigboss_an Rookie DRN Member

    Joined:
    Sep 21, 2005
    Messages:
    35
    Likes Received:
    0
    Trophy Points:
    0
    Desperate for your help! This is a well maintained 2003 rm125 that I can't figure out. Most of the time it will start, run for a minute or so and then stall. Let it sit for 10 or 20 minutes and will do the same thing. I checked the carb, it's immaculate. Jets are clean, float and float height are perfect. Fuel flow is perfect, also replaced fuel with fresh fuel. Compression is good, reeds are like new (VForce). Replaced spark plug with known good one. I do not know the exact numbers for the coil, cdi and stator. But i do get measurements that appear to be ok. Is it possible that one of these runs for a minute and then gives out (can they warm up for some reason)? I have never seen one go bad that way. They usually work or they don't (or am I wrong here?). If it's one of these, which would be most likely? I also tried disconnecting the kill switch. Oh, when it runs, it runs perfectly! Is it possible that the crank case fills up with pressure? I know I'm pushing it a bit, but I'm desperate. When it stalls, it's the usual 'bwaaah bwaaah' as if it runs out of fuel.
    Any ideas? Thanks for your help.

  2. bigboss_an

    bigboss_an Rookie DRN Member

    Joined:
    Sep 21, 2005
    Messages:
    35
    Likes Received:
    0
    Trophy Points:
    0
    Update: we rolled the bike down a long hill and as soon as it started I let it scream as hard as it would go. Did this three times. On the third try, I noticed that it would remain started for longer periods. Finally, it started to run as long as I kept it at very high RPM. Eventually things settled down and we saw a bizarre white smoke coming from the exhaust, as if the silencer was on fire. The more we ran the bike at its limit, the better it got. I'm guessing that the owner just ran it too slow causing a build-up of oil deposits on the power valves and/or exhaust. I will take it out to the track over the weekend and see if it runs ok. Hopefully, another satisfied customer. If you don't see a follow up post on this, assume that problem is solved. Thanks to those that at least read my post.
  3. arnego2

    arnego2 Member DRN Member

    Joined:
    Mar 8, 2008
    Messages:
    270
    Likes Received:
    1
    Trophy Points:
    18
    glad you found it. I had guessed a dirty fuel filter or the vent valve of the tank but then discovered your second post. Powervalve issues should not make it run and stall normally.
  4. bigboss_an

    bigboss_an Rookie DRN Member

    Joined:
    Sep 21, 2005
    Messages:
    35
    Likes Received:
    0
    Trophy Points:
    0
    Hello arnego2, actually the bike came to me without the vent hose on the tank (that's why I suspected water in the tank may have caused the stalling, I was wrong) and one of the first things I checked was fuel flow from the tank. You're right, it looked like the engine was starving for fuel and so I checked and rechecked those issues first. I agree that powervalve issues should not cause it, but after letting the bike scream it's guts out, things got a lot better. Then what was it? I haven't fixed anything really. Could a clogged exhaust be causing too much back pressure or something like that? Or is there any way there was a buildup of oil or gunk on the bottom of the crankcase because of the bike not being ridden hard enough over a long period of time? When the bike was ridden hard for a little while, there was a huge amount of smoke at first. Anyway, we'll find out this weekend. Thanks for your time.
  5. arnego2

    arnego2 Member DRN Member

    Joined:
    Mar 8, 2008
    Messages:
    270
    Likes Received:
    1
    Trophy Points:
    18
    long story

    As you just got the bike I would suggest to give it a complete overhaul should you plan on riding it. First the issue you got on hand. You are right a clogged exhaust and/or silencer can have some bad effects. I'd change the fuel too if it was in there before I got the bike. You never know how old that stuff is or if someone played a bad trick on it, someone unknown to the previous owner even.

    Even in a well maintained bike my first look would be at the top end. Some people maintain their bikes just for the eye :bang: other are more thorough. :blah: :blah: On a 125 the top end should be done every 10 to 20 hours for a reasonable experienced rider.

    I also would change the bottom end roller bearings, the respective oil seals and the needle bearing of the conrod. If the previous owner has some bills to proof he's done it recently than sure one should take the gamble.

    I bought a rm125 a few years back when I started and I was told the piston looks great, it took me about 12km to proof them otherwise. I did the bottom end plus a fresh replate of the cylinder and some other parts I found. I repacked the silencer regreased suspension bearings and replaced those which were bad. New fork seals and cleaned the stearing bearing.

    It was well worth it, the bike was great, I sold it to a kid who neglects the bike and just tries to make it pretty.
  6. EncyclopediaRonnie

    EncyclopediaRonnie Rookie DRN Member

    Joined:
    Nov 8, 2010
    Messages:
    142
    Likes Received:
    0
    Trophy Points:
    0
    repack sliencer this should be done just as much as a top end re ring 20hrs should be rings on a 125 and id repack at teh same time, u can hear packing as it goes the bike gets way loader and crakier
  7. T-Bone

    T-Bone Subscriber

    Joined:
    Feb 10, 2001
    Messages:
    155
    Likes Received:
    0
    Trophy Points:
    0
    Any update on this ?? I interested in what the problem was . I was thinking a leak in the head and maybe rad fluid coming in .
Similar Threads: RM125 starts
Forum Title Date
2-Stroke Discussion 96 model RM125 Jun 17, 2014
2-Stroke Discussion Is my Air Screw Missing? (RM125) Nov 25, 2013
2-Stroke Discussion Cylinder for 2003 RM125 Questions Nov 7, 2010
2-Stroke Discussion rm250 stator on a rm125 Aug 22, 2010
2-Stroke Discussion 1994 Rm125 Jun 14, 2010

Share This Page