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TTR125 Hard starting - end all thread

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TTR 125 Hard starting causes/checklist:

Carb issues:

  • Bikes are extremely lean jetted for EPA.  THis makes them very cold blooded and you have to leave the choke on for a long time on a cold start.  To remedy, install  a 17.5 pilot jet (Yamaha OEM - 5HP-14142-17-00)
  • If your carb has the fuel screw capped, you need to remove the cap (either drill it out, or use a deck screw and pull it out with pliers).  Then you can adjust it
  • If your bike has been sitting and with fuel in the bowl, you need to do a COMPLETE carb clean. This includes the jets, passages in the carb body and bowl - including removing the fuel screw.  When done, put a light film of grease on the choke plunger so that it doesnt seize in the bore
  • Check the float height and also the float needle is seating and not leaking.  Replace as needed
  • Check fuel coming from the tank!  Also after 10 years, good idea to replace the fuel line as it will start to disintegrate internally and plug up the carb.

Electrical issues:

  • pull the plug and check spark.  Replace plug as needed
  • pull off the spark plug boot from the coil wire, inspect, possibly trim the wire back about 1/8" and reinstall the cap by twisting it on
  • disconnect the kill switch - may have a short
  • Test your CDI and Stator.  Refer to service manual
  • Check flywheel and flywheel key

Engine issues:

  • valves - check and adjust clearances
  • compression, do a check
  • intake boot after time will need replaced along with gasket/oring for it
  • Air filter, clean inspect replace as needed.  You can also uncork the bike by removing the baffle from the top of the airbox
  • Check muffler is not obstructed

 

If anyone wants to put in helpful links to service manual pages or vids on these topics to make a great sticky, please feel free to!  Hope this helps and keeps the "TTR125" not starting threads to a min

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Thank you, quite helpful, new fuel screw was done with jets, will replace the fuel line. 

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Addition:

 

  • If you have rebuilt the motor, check the cam timing.  Again refer to service manual
  • On the intake boot, there is a capped vacuum line.  Replace the cap every few years.  Otherwise you will have a large air leak!

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bringing this back to the top. 

Again, bikes are jetted lean.  update the pilot to a 17.5 or get the jet/power kit from RMATV that has it in there. 

If you are storing the bike for more than a week with ethanol fuel, drain the carb bowl!  the pilot jet is the smallest jet in the carb and plugs VERY easily. 

Winter storage, again, drain the carb & and add ethanol gas stabilizer to the fuel!  if you want to be double sure, also disconnect the fuel line from the carb.  This will make starting in the spring easier. 

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