Home Forums Shifter Karts 99 CR125 not starting

This topic contains 7 replies, has 4 voices, and was last updated by  Sanford Mitz 3 years, 10 months ago.

  • Author
  • #52586

    Brad Alan

    I recently purchased a 99 CR125. I had it running and I raced it at Grattan earlier this year. It was a blast!


    Anyway I got home and I couldn’t get it running again. I did get it pretty hot during the race. I took the top end and cylinder off and noticed a little wear in the piston from the bridge on the exhaust port nothing alarming. I ended up putting in a new ring.


    I I got it all back together and it ran for about 3 seconds. I put the strap around the wheel and gave it another pull and it fired a couple time then back fired pretty good…  I pulled it a few more times and nothing…


    Any insight on what I should troubleshoot next?



  • #52589

    Brian Spek

    had a similar issue.  first check to ensure a good spark.  throw in a new plug to be sure and get the plug grease to ensure a good fit with the boot and no arc’ing.  Then if that’s ok, go to the fuel system.  Mine started running again after rebuilding both fuel pumps, and replacing the pulse lines.  empty these after every race.  Also, if someone accidentally used the wrong oil, or a low oil-fuel ratio, it can cause problems.   if all else fails, check stator in case it was knocked out of synch.  also check all ignition connectors.

  • #52609

    Alan Sheidler

    Non-starts can be caused by:

    Low compression, or fuel or ignition problems.

    We had a non-start issue once which was caused by a failed ground strap.  The wire was coated, so we could not see that it was broken internally.  New ground installed, started instantly.

  • #52612

    Sanford Mitz

    You need fuel, spark, and compression. Check the compression and make sure you do not have a broken reed. Even if you have someone pull it in sixth gear and put your thumb over the spark plug hole. Be sure to ground the plug. Next check for spark. Pretty hard to see on a CR125. Ground the plug and cup your hands over it while someone spins the rear wheels. If you have that, then the box, stator, coil, and grounds are good. The last is fuel. Is the plug wet or dry? If its really wet, you also may have the bottom of the crankcase full of fuel. Ground the plug and spin the motor with a strap off of the wheels with the plug out. If you are flooded below, you should see a mist coming out of the plug hole. If so, put in a dry plug either new, or known good and let it go. You can also try turning it over on a start with the accelerator all the way down. If it catches, be sure to let up. CR125’s are really reliable and should not be hard to start. Check out some of these items and report back.


    • #52704

      Brad Alan

      All – Thank-you for all of the comments and suggestions.


      First, I checked the spark.  Ok there.

      Second, I checked the plug, no fuel… Hummm.  I cranked it over a few times and didn’t see fuel moving past the pump…  I had a spare pump so I put it on.  I blew some fuel thru it, and it started on the second pull.  Ran fine after that.

      I will be rebuilding the fuel pump I took off tomorrow.

      Thanks again!

  • #52705

    Sanford Mitz

    Be sure to clean out the pulse line. When you look at the other pump, check the pulse side for being full of fuel.

    • #52708

      Brad Alan

      Sanford, I will look for that. If the pulse line input on the pump is full of fuel does that mean I should look at/fix something else within the engine too?


  • #52710

    Sanford Mitz

    No. Fuel accumulates in it and part of regular maintenance is to wash\blow it out. I don’t know where your pump is located, but check the line for cleanliness. This is the one that goes from the nipple on the side of the reed cage to the port on the pump. This sends the pulse to the diaphram in the pump to pull\push fuel. Check for a nice short routing of the line and usually you want the pump higher so fuel can drain back. Keeping it clean will make fuel delivery more efficient. Also make sure there is no kinks in it and that you are using a fairly thick walled type of tubing.  Some people use the one with the braid in it, or Motion-Pro which has a super thick wall to prevent kinking.

You must be logged in to reply to this topic.