Question about 2003 Yamaha DT 125 R

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Hello ive recantly replaced my pistons and rings on my dt 125. i have been told it was the pistons that was stopping my bike from running, but now that i have changed them my bike will still not start. can you help me out and give me some problems that it could be thats keeping it from starting. thank you...paul...

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The first thing to do is get a new stock spark plug. Hook up the plug wire then have someone kick the lever while you hold the metal side of the plug against the bare metal cylinder head looking for spark while the starter is being kicked. If no spark is seen, find out why. Use a meter to check the handlebar and side stand switches for proper operation. How good is the battery? Are there any wires abraded or disconnected? Has the pulse generator, coil or CDI gone bad?
If spark is present, Be sure the air cleaner is clean. A dirty filter restricts the air the carb needs. Okay, you have spark and you have air, now you need gas. Start by draining the carb. Condensation from the gas tank can get into the carb float bowl and build to the point the carb is feeding only water into the engine. Engines don't run well on water. When starting the bike, do not go nuts with the throttle. Every twist on the throttle sends a shot of gas into the engine. Too many twists can flood the engine. Your bike is water cooled. Good gaskets/seals are needed on the cylinder and head. At this point we will assume the coolant system is not leaking.

Posted on Mar 22, 2011

Testimonial: "thank you so much for the advice, ive checked everything that you've mentiond on ur list, but it is still not starting, can u sugest anything els.thnx"

  • tombones Mar 23, 2011

    Do you have spark??? New plug? clean air filter? The gas IS turned on isn't it? Check each fuse with a meter, one could be blown. The kill switches are working? Check for loose and disconnected wires. If the bike still has no spark, take the bike to the dealer and ask them to check the coil, pulse generator and CDI. If you do have spark, get a can of spray starting fluid and spray into the air intake ( air filter ) then try starting it.

  • weepettinger
    weepettinger Jun 16, 2012

    SEE IF ur earth wire on ur bike is contected it happened to mine before but no i have changed my pision and head gasket and now it will not start


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Check your ex it ma be plugged coment on bike nothing to do with spark I did not give any info on spark matter just why it might not run and rev.

Posted on Dec 18, 2011


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Have i broke my bike by moving power valve whilst running now its not starting

Hi, Anonymous I don't think so probably just flooded remove the spark plug kick it over a few times squirt some Brake Kleen or starting fluid on the plug and blow dry with compressed air and reinstall and you are good to go for more information about your question and valuable "FREE" downloads that you will need please visit the websites below. Good luck and have a nice day.
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Apr 30, 2014 | 2003 Yamaha DT 125 R

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Jun 21, 2010 | 2000 Yamaha DT 125 R

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Is your bike making blue/blueish smoke while running? From the stuff you told us, it is either worn piston rings or worn valve seats, but i would personaly bet it's the valves, because the knocking sounds would be the valves being severely out of adjustment, leading to a huge loss of power and many noises. Hope i helped you :)

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DT 125 2000 Very poor starter. Stolen recovered so no ignition

had exactly the same prob with my dt 125.

In the fuel tank there were two filters that had become a little blocked with small fragments. I replaced both of these, aswell as the petrol tank and now works perfectly.Worth replacing with every service.

Also make sure the amount of fuel to oil is correct because if there is too much oil it leaves a small layer of oil on the spark plug which gets thicker when the engine cools. When you dip the spark plug in petrol and put it back in it obviosly makes a large enough spark to remove the oil, but repeats itself when the bike cools.

Hope this helps


Apr 15, 2009 | 2000 Yamaha DT 125 R

1 Answer

Cogs in a gear box

hi karen, that is right, i do have a DT 125 myself and same thing has to be done.

Usually this is balance the engine so that the moving parts will move to a limited place. this is also to avoid further block damage when the piston is moving up and down.

Jan 01, 2009 | 2002 Yamaha DT 125 R

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