Yamaha TTR 125 Won't Start


One of Yamaha's small, speedy dirt bikes, the TT-R125 is a motorcycle meant to appeal to large kids and adults alike. With a smaller 124cc engine and a lightweight frame, engineers designed this bike to be particularly maneuverable on the course. Its eleven inches of ground clearance, however, makes it a contender on trails as well. For minor repairs, Yamaha offers tips in its service manual to guide owners through the process. In particular, trouble starting the TT-R125 could involve maintenance in one of two systems.

Things You'll Need

  • 10A fuse
  • Continuity tester
  • 12 volt, 3.2 ampere-hour battery
  • Standard wrench
  • Battery tester
  • Battery charger
  • Unleaded gasoline
  • SAE 10W-40 or 20W-40 engine oil
  • Spark plug wrench
  • NGK CR7HSA or DENSO U22FSR-U spark plug
  • Spark plug gap tool


  • Operate the TT-R125's electric starter. If the engine won't even turn over, then there is likely trouble with the starter.

  • Inspect the bike's main fuse, located underneath the battery cover on the left side of the TT-R125. Remove the fuse and connect it to a continuity tester. If the tester indicates that the fuse is blown, replace it with a new fuse with an amperage rating of 10A.

  • Try the starter again. If the engine still won't turn over, move on to an inspection of the battery.

  • Remove the battery, located underneath the battery cover on the left side of the bike. Disconnect the negative (-) battery lead first, then the positive (+) one. Undo the battery straps and gently lift it away from the bike.

  • Inspect the battery terminals. If they are corroded, scrape corrosion away with a wire-bristle brush. If corrosion persists or if the battery is otherwise damaged, replace it with a new 12 volt, 3.2 ampere-hour battery.

  • Tighten the battery connections using a standard wrench.

  • Test the battery's charge with a pocket battery tester. If the voltage is lower than 12.8 volts, charge the battery to this voltage using a separately-powered battery charger.

  • Reinstall the battery, this time connecting the positive lead first and the negative lead second. Reinstall the battery cover.

  • Operate the TT-R125's electric starter. If the engine still fails to turn over, take the bike to the shop to have them inspect the starter motor.


  • Check fuel levels first if the engine does turn over, but the bike still won't start. If they are low or empty, refill the fuel tank with unleaded gasoline and restart the engine.

  • Inspect the condition of the fuel in the tank if the engine still won't start. If it is gummy or watery, it may be stale or contaminated. Take the bike to a mechanic to have him drain the fuel tank and refill with fresh gasoline.

  • Check engine oil levels by placing the bike on a level surface and removing the oil cap and dipstick. Wipe the dipstick clean, re-insert it into the fuel tank, and remove it once more. Engine oil levels should be between the minimum and maximum marks on the dipstick. If not, fill to this level using SAE 10W-40 or 20W-40 viscosity engine oil.

  • Remove the spark plug if the engine still won't start, located in the bike's single cylinder. Undo the spark plug cap by hand, rotate the plug counterclockwise using a spark plug wrench, and gently lift the spark plug free.

  • Inspect the color and condition of the plug. If the electrode is white and brittle, black, or cracked, replace with either a NGK CR7HSA or a DENSO U22FSR-U spark plug.

  • Set the spark plug gap to 0.24 inches. This gap is the amount of space inside the hook at one end of the spark plug. If it is too wide, shorten by pressing the plug against a hard, flat surface. If it is too narrow, widen with a spark plug gap tool by gently pulling the hook wider.

  • Reinstall the spark plug and plug cap.

  • Try the starter again. If the engine still won't start, take the bike in for inspection.

Tips & Warnings

  • A Yamaha dealer is best equipped to deal with major repairs if troubleshooting fails.
  • Never handle gasoline or a battery while smoking, as this can cause explosive fumes to ignite.
  • Battery acid can burn skin and eyes. To avoid burns, wear gloves and goggles while inspecting this system.

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  • Photo Credit car fuses image by Witold Krasowski from Fotolia.com
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