Bought DT125X, cannot get it to start? Spark, fuel OK



  • Hey,

    Now, here's what I tried:
    -Cleaned air filter
    -Cleaned carburetor (It wasn't that dirty) (Has 17,5 air and 220 MJ in it which I think will be too small, considered that the snorkel is removed)
    -Cleaned battery + and - terminals, on the relay etc, fuse is ok.
    -Removed ignition coil from frame and cleaned terminals, and I measured it with Ohm meter:
    -->Primary: 0,5 ohm (manual says that it should be 0,23 ohm, so would this mean that the coil is faulty?)
    -->Secondary: 8kOhm (manual says should be 7.9 So i guess this is ok)
    -Spark plug is BR8EG (I will upgrade to B9ES soon) but I think it was replaced when the engine was rebuilt as it is clean.
    -Measured plug cap, it has 5.4 kOhm which is great.

    Now, I have strong spark on the plug, white or bright blue-ish color. I can even hear it popping. I tried injecting cold-starting spray and even a little fuel in the cylinder and bump starting it with a help, but it just does not want to start.

    When I put the side stand down or flip the switch to "off", spark is gone so I guess these switches are ok and neutral works also.

    Now one thing I haven't tried and I can think of: The petrol I'm using is still the one that is in the bike, I dont know how old is it, max 6 months I guess but it isn't stinking like old petrol does. I think that when the engine was rebuilt, they replaced crank seals so that won't need attention. I don't have compression meter but with two people we can barely do the bump starting so I guess it should start.

    Background story:
    I just bought a 2006 DT125X 2 weeks ago. The seller told me that the bike wasn't started for 3 months, and that the engine got a full rebuild at the official local Yamaha service 90km ago (the trip counter was zeroed when the rebuild was done) I went to see the bike, he told me that the battery was broken so I brought a 4Ah battery with myself which was not enough for the starter to spin for long. We tried to start it off a car but the starter motor broke (it turned out when I got home and disassembled the motor that the coil is broken inside, so I ordered a new one off ebay, until then I have to bump start the bike somehow. We tried bump starting it there but with no success. Despite the non starting bike, I got a good deal on it, and overall the bike is almost in mint condition, with no major fabrications. Later it turned out that it has a Gianelli resonator with stock silencer on it.

    Now, my main concern is this line:
    -->Primary: 0,5 ohm (manual says that it should be 0,23 ohm, so would this mean that the coil is faulty?)
    Do you have any other ideas, please?



  • Usually side stand switch is the culprit. You usually find that the spark is intermittent, at times the bike almost splutters into life.

    Otherwise the cdi could be going bad.

    Generally if its got fuel air and a spark then it will run. I am inclined to say this is an ignition fault from your description, otherwise it would run.

    The amount of times I have read/heard yamaha rebuilt and it turns out to be bullshit....so take that with a pinch of salt.



  • If it were the side-stand, I would be able to start it in neutral with a working starter, as it turns the bike off only in gear when you release the clutch, am I right? Anyways, it won't even try to come into life, I don't hear a single "explosion"

    As for the cdi, you are talking about the black box under the fuel tank right? That costs more than 100 euro for a used unit 😞 I hope it is not broken, any way to test it other than changing it?

    I agree that despite the fact that the DT125X is a "stupid 2 smoker", the electronics are not so simple on it, and I hear that too that there are problems with it.

    Also my bike only has 26 000km on it overall. (=16 000 miles)

    Later this week, I will try to fill it up with fresh fuel, the new plug, and I see something in the manual called source and pickup coil tests. I can measure them though the wires. But if they are faulty, are these located in the ignition base where the coils are?



  • @Lorant2 The side stand switch has been known to cause problems, in gear out of gear up or down. And can be often sen unlooped.

    The other one could be the neutral switch. But that's connected to the clocks so you would see the neutral light go out and I've yet to see one go faulty.



  • I'd definitely try some fresh fuel 👍



  • I just measured the alternator coils.
    -Pickup coil is 285 Ohm (should be between 280-420) so its ok.

    -Source coil is 750 Ohm (should be 192-288 ohm) so I went further:

    --> removed the left side cover (in DE06 the magneto stays on the crankshaft and the alternator stays in the cover)
    --I saw that 3 wires are connected, there is 2 soldering on one of the sides, measured that and it is ~749 Ohm, so it is not the wire that is broken or connections.

    ->Also, that source coil has gotten loose off its "iron" base, so I guess that is the problem here.

    -2004 alternator
    It has a lot less coils so I guess I cant replace it and also it was fixed on the engine rather than cover.

    2004-onwards alternator
    The cost is hella lot 😞 And there is no guarantee that it will work.

    What do you guys think, can a specialist recoil that source coil for me? Or is there any other cheaper way to repair this?

    BTW thank you for your answers! 🙂

    EDIT:
    TDR91-02 alternator
    It looks the same as mine, even the connections, and ebay page also says that it is compatible with the DTX, I guess it is compatible because both have starters and Yamaha just used the TDR base on the later DT's. Would this mean that I can search a guy locally with a cheap torn down TDR and replace it?

    EDIT2:
    Imgur pictures of the coil

    EDIT3:
    GDrive video of the loose coil

    EDIT4:
    Talked to 2 guys, one said that it is common among newer DT ignitions to go faulty, and that a working stator is really rare and expensive. He recommends me to convert to some old ignition, I can even keep the e-starter, I need CDI, stator, magneto, regulator and wire harness. All this he can give me to 100 euros cost. What do you think?



  • @Lorant2 BR8EG and B9es is not the correct spark plug. You should use BR8ES or BR9ES. Could be your issue.



  • @Bananper Yeah I wasn't convinced that either, but it's been so long since I've worked on the DT I had forgotten.



  • Okay, I will try it then, but I guess the yamaha service put it in. On the internet I found out that I EG differs only from ES that it is a "racing" type plug with a thinner electrode that is less likely to get fouled. But I will try fresh fuel and Br9es when I have time.



  • Got the new stator, still can't bump start it. The only difference is that I inject fuel at the plug, It will try to start for a few strokes. Also got the new plug, BR9ES with 0.6mm gap. Stripped down the carb again, it is clean, and tried it with fresh fuel, still nothing. Intake manifold looks ok, and tried to see inside with flashlight, and membrane looks okay too. If I take out the plug, it is not soaking in fuel, so it is not getting fuel, despite trying to bump it with choke on. I am hopeless now. Compression is okay I think because it is really hard to push even for two people.



  • @Lorant2 Is the plug sparking? Take it out, connect it to the HT lead and place the tip against a metal surface. Crank the bike with the kick starter and look for a spark, it will be very visible for a split second. If there's a spark then the plug is getting voltage, if there's nothing then you have an electrical problem.



  • @NINJA I dont have a kickstarter. But I can check the spark by putting it in 6. and bumping the bike whilist looking at the spark. With the previous stator it was whiteish as I have written it, but now it is more of a blue.



  • @Lorant2 OK that's fine, so you're getting a spark and fuel, what's the air situation? Is the carb working OK?



  • @NINJA I cleaned it completely, even removed the atomiser tube to make sure the holes arent blocked. Gaskets are fine it is not leaking and fuel level is correct. Has 17.5 air jet and 220 main jet which might be small considering that it has gianelli but it shouldn't be a problem to start it, especially since it has run with this setup for the previous owner. Power valve servo works as it checks, and it is set to the mark on the cylinder.



  • Did you clean the choke passageway in the bowl?



  • Also, have a look at the reedvalves for broken or torn reeds.



  • @Lorant2 Sounds daft but it happens more than people care to admit too. Is the engine cut-off switch activated? If it's turned 'off' then check the wiring, is there an earth to it, check that to see if its rusty???



  • I checked the choke and it is not blocked, I blew it eith compressor. I will have a look at the reeds the following day. But I took a picture inside the intake manifold and it looks ok, I will have a look if it has increased gap then I will replace it, they are moving freely as I touched it gently with my hands. I will check if I can see through it, but then again that would cause flooding I think and my plug is not oily at all after bump starting it for meters.



  • I cleaned all the earths a week ago when I was diagnosing the starter motor. The earth is clean on the battery, on the engine, on the HT coil and on the regulator too. If I set kill switch to off, then I dont have any spark, neither if I let my side stand down.



  • @Lorant2 So if the kill switch is in the 'off' position, aka not turned on and the side stand is up - then you get a spark???


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