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

  • I mean that it works as it is intended. I turn the ignition key to on, power checks, and the kill switch is set to "run" I guess (I think it is pressed from the top to the bottom), anyway it is working as it is written on it. I believe this is not an electrical issue anymore, my plug is just not soaking in fuel and oil as it should despite the (I think) big compression. Tomorrow I will also have a friend to come over and we will check the exact PSI compression, what should be a correct value? Above 100, with full open throttle?

  • @Lorant2 OK well it's another issue then. You can download the service manual for free from here;

    And well worth the money is a Haynes manual;🇵🇫1&frcectupt=true

    Both have lots of tips and troubleshooting guides!!! 😉

  • Some update:

    I have removed everything again, reeds are perfect, intake manifold too. Boost bottle was a little loose so I replaced the clamp on it and it is better now, and managed to start the bike with a catch LOL 😃

    I put it in 6. , turn off ignition and bumped it a lot with choke on, then put it in 3. and managed to start it and rev it a little till I dropped the gas and it is not starting again. Also it was smoking a lot but it was revving freely and dropped the rpms nicely too like theres no air leak. I will try to further investigate it.

    Also I had the air screw open at only 1/4 turns now. It was on 1 turns before and completely closed when I first disassembled it.

  • @Lorant2 Improvements then? The smoke was probably from the excess fuel aka flooding from repeated starts. Try the electric start with no choke if it feels sluggish to start, crank it a 8-10 times then add choke.

  • As fot cleaning the choke, as I said theres a passageway in the floatbowl, thats often overlooked when cleaning carbs, as people focuse on the main body. Im not talking about the choke plunger and where it mounts in the carb.

    Just another thing to exclude

  • @Jens-Eskildsen I did blow that too. I started it today too and went for a 10km ride. Couldnt get it past 70 kmh. Removed exhaust, and saw that the power valve does not opens despite it is turning on ignition. It was rotated by 180 degrees, I think they installed it incorrectly in the service. Also, found another major problem, one huge piece of the upper piston ring is teared down 😞 So i will have to disassemble the cylinder and replace the rings/get a new piston and rebore. I might be lucky that it tore off the front where only the exhaust port is and it got out. Also it was smoking quite hard while riding and it was working better with choke on. On low rpms it felt as it has air leak, on high rpm it didnt rev I think because of the power valve misfunction.

    Am I right that only Athena and original head gasket is recommended to use?

    And how hard is it to replace the right side crank seal? Does it need removing the whole clutch or just the little cog on the crank? For the left side I have to make a flywheel puller plate as I see.

    Also, I currently have 220 MJ and 17,5 Pilot jet, am I right that I should start out with the standard DT125R setup 25 pilot jet and 240 main?

  • @Lorant2 Sounds like the PV was hitting the piston which would explain a lot of what's going wrong with your bike. I'm glad to hear that it ran eventually, a top end rebuild would eliminate a lot of problems for-sure. And yes Athena or OEM gaskets are the best, personally I feel Athena are the best ones. Check in the manuals I mentioned before to see about replacing those seals. I would do those repairs and anything else which you find faulty whilst fitting those new parts and then see where you are with your bike? Before you go spending lots more money on other parts, which may be OK for now. 😉

  • A frriend had to replace the right crank seal, he did it from the outside.

  • Okay, thank you, I will take off the cylinder and look into the top end. If it was really rebored 100km ago and the cylinder is not hurt, I will be trying to order a correct size piston ring for it and check if the power valve hits the piston and if the cylinder ports are "shaved down". I think I will be replacing the two seals too and then see what the bike does.

    I was thinking about the same anyway, that the rotated power valve hit the ring, but then again it would have destroyed the bottom ring too. Also as I know, some older DTRs were restricted with a diamond shaped power valve which had to be rotated too.

    imgur gallery
    Before it was rotating but it was not changing, and on the other video it is rotated and aligned to the mark, I then further adjusted it to be in one with the cylinder.

  • @Lorant2 Check and clean the PV's cables and connections as well. Sometimes they stick or rust up and stop the PV from operating.

  • Some update:

    Imgur gallery

    It is not on first oversize, but on the third one, 57.50. The cylinder looks like it was bored recently, it is still "matte", and the piston inside is "RAM" branded which you can get for 20 euro here. The problem is not the bad quality piston however.

    They should have checked if the power valve has enough clearence to the piston. They definitely forgot this. As you can see, it is stucking at a point so much that I can't believe how it did not snap the second ring too.

    Now, as the piston clearence is fairly big, but the engine was having a great sound, I will order a new piston that is the same quality as this (I have positive experiences with this brand in other bikes) and I will grind off a little off the PV, then assemble it with that, it still hasn't run in so I guess that I am safe to replace the cylinder. If it will be tight, I will take it to a cylinder bore specialist. And if it will start to rattle or become weak, I will take it off again and get the last size 58.00 bore with a Meteor piston.

    Also, my starter motor arrived too! I just tried it, it spins the engine quite fast 😁
    I might have the piston here by friday, and then I can work on it on the weekend. Also ordered a 25 PJ and 250 MJ for the bike (because it has gianelli and cut off top airbox) which will be here.

  • @Lorant2 See here for more info which may help you out;

  • Yeah common problem. Powervalve needs to be modified at that overbore size.

  • I just have contacted the local Yamaha official service by email. The bike was indeed serviced at them. But they only did the top end, I guess the bottom was made before that. They told me that a prox piston was installed, even though they only charged the previous owner like 70 euros for it which doesnt even cover the prox piston price, so I guess thwy just installed this 20 euro RAM piston. It is a mess that they just went over the fact that the power valve was definately hitting the piston.

  • Definitely should have known to modify the valve, that's a well know thing on YPVS engines.

  • @Lorant2 Sounds like a right bodge job! Sadly it seems that you will have to sort their mess out.

  • I believe they mostly do 4 stroke engines nowadays in a yamaha workshop, it was maybe too easy for them lol 😃
    I am doing my best to bring this bike back to life, and planning to keep it for a few years as I wont be having more money for a newer one in a while.
    The piston is arriving tomorrow, I will make a video of the bike running if I manage to assemble it in the weekend. Main and Pilot jet arrived today 😃

  • @Lorant2 At least you will have peace of mind once it's fixed properly and some bike history as well too. 😉

  • Managed to start it, has a nice engine and exhaust aaand airfilter sound 😃

    It is running smoothly so jetting is almost correct and needle position too, also starts if I just tap the starter button even without applying throttle. Only problem is it smoking if I apply full throttle, so I will have to adjust the air filter as it was cut open but a plate was glued back with 4 small holes, it has a mesh on the top of it for a little filter effect so I will just drill more holes later, also my plug is dark brown, needs more air.

    I painted the resonator, and applied some exhaust gasket on the cylinder connection so it is not leaking, but it is missing the silencer rubber and the pipe that is part of the stock silencer was torn off at the welding so I will have my father to reweld it for me, then I paint that too.

    Also applied some 10W universal indicators to rear because someone replaced them with 21W and the hazard switch wasn't working that way.

    Engine sound
    Startup like a boss

  • @Lorant2 Sounds good bro, it looks like you are back on track for some summer fun!!! 😎 😎 😎

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