Yamaha DT50

Discussion in '2 smokers' started by Dave in Wi, Apr 21, 2020.

  1. Dave in Wi

    Dave in Wi Long timer

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    This set up will make my back feel much better. Not entirely sure why I didn’t think of this this morning. Other than, I really didn’t think it would take this many times to flush the tank out. Lesson learned, I should have started with some mechanical agitation with BBs in this to begin with. And, I should’ve rinsed it out much more thoroughly with the hose before I went to flushing it with gas. I really didn’t think the tank was this bad, I ended up being much worse than I thought.
    #21
  2. Dave in Wi

    Dave in Wi Long timer

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    Here it is, about 4 PM. I rinsed another 2 gallons of gas and ATF through the tank about 2 cups at a time. It finally came out clean. I did notice that the gas tank is formed with what appears to be a sediment trap. There is also a sediment trap built into the petcock.

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    Speaking of the petcock, I am going to order a new one. The rubber parts are cracked and the screen for the reserve position is broken. I can get the new rubber parts as a rebuild kit, but it comes to the same amount as a full at fuel cock assembly. So I’m going to order one up, I hope I find that it is truly available.

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    To those that are familiar with this bike I have a question. Going through the carburetor section of the repair manual, it shows how to measure the clearance on the read valves. Is this something that I should really check?Or is this something that never goes bad. The reason I ask is, it says to use a new gasket if you take this apart. I’m not opposed to doing it, I just want to know if I’m wasting my time or not.
    #22
  3. Anachronism

    Anachronism Lived Too Long

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    @Dave in Wi : No one else on here will agree, but I never touched the reeds on all three of my DT50LCs.
    When I removed the carb to clean on the last two I simply shone a light into the rubber connector to verify nothing obviously wonky.
    If it looks like someone has been in there before you it is easy enough to check.
    Stock reeds last forever on these engines.

    Are you coating that tank inside after all that work?
    As long as you keep it full of fuel at all times it should stay shiny.
    My last two tanks were ugly on the inside.
    I simply cleaned the screen on my petcocks & added inline filters.
    Sadly , 31 year old metal tanks rust.
    #23
  4. Dave in Wi

    Dave in Wi Long timer

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    I am not planning on coating the inside of the tank. I have read a lot of horror stories about coatings failing. This is only the third tank that I have had to de-rust so I don’t have a ton of experience. My feeling is, you need absolutely meticulous prep work to get a coating to stick. I spent a ton of time on this, but I don’t feel like it’s perfect enough for failure-free coating. And if a coating fails you have a real mess on your hands. My feeling is, as long as there are no pinholes I’m going to try to get away without coating it. Keep it full of ethanol free gas and stabilizer and it should be good.

    The big issue is disuse. When I first got this bike I used it occasionally every summer, riding it every month or so. Then it ended up at my parents cabin, stuck in the back of the garage. It wasn’t easy to get to, so I didn’t use it for years. My plan now is to keep it at my home, where it’s easy to get to and I can take it for spin every so often.
    #24
  5. Dave in Wi

    Dave in Wi Long timer

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    So here’s a question. It’s more of a general oil injected two-stroke question but I’ll give it a shot.

    To remove the carb I had to disconnect the oil line. The service manual says when this happens you need to bleed the system using the oil injection pump. When I start it up should I start out using pre-mix? Seems like I should, until the system is primed.
    #25
  6. Anachronism

    Anachronism Lived Too Long

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    @Dave in Wi : If you have the oil handy it can't hurt but for a little extra smoke.
    The only time I disconnected my oil feed hose was on my third DT 50.
    I removed the oil injection completely as the pump was leaking profusely & went to premix permanently.
    #26
  7. Dave in Wi

    Dave in Wi Long timer

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    I’m trying to be patient waiting for the new fuel cock. I know shipping parts is hit and miss these days. It took quite a while to get the carb parts I ordered before. (And I’m still waiting for the levers. Luckily the old ones work and won’t keep me from riding.)

    I’m having a PBR and assembling the carb. I set it aside when it got super hot and humid last week. Also spent a little time cleaning nooks and crannies while the tank is off.
    #27
  8. Dave in Wi

    Dave in Wi Long timer

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    IMG_2141.jpg

    Yay, new fuel cock just arrived. Fingers crossed I’ll be able to start it up this weekend.
    #28
  9. Dave in Wi

    Dave in Wi Long timer

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    New levers just arrived!
    #29
  10. Dave in Wi

    Dave in Wi Long timer

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    I spent the morning installing the carb, new fuel lines and filter. I rinsed the oil out of the tank with some of my chainsaw prefix. Got the tank back on, and put in the new battery.

    Good news, it runs! It seems pretty cold blooded but it seems to run ok. Maybe a little down on power from what it used to be, but it’s been a long time since I rode it so who knows.

    I rode it around the neighborhood for a while. Bad news, the headlight and turn signals are not working. They used to when I parked it so I’ve got some work to do before it’s technically street legal. I need to pick up a new multimeter. Electrical isn’t my thing, but hopefully it will be relatively easy to figure out.
    #30
  11. rd400racer

    rd400racer Long timer

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    I was actually given one for free when I picked up this SR540 race bike (for $100). I didn't feel like screwing with it so I gave to to a friend that had it running within an hour. That's OK, he's fixing my YZ250 for free. That's how I roll, the barter system:D By the way, he said it's a blast to ride.

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    #31
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  12. Dave in Wi

    Dave in Wi Long timer

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    I bought a new Northern Tool multimeter and started the diagnosis process .

    I bought a factory manual pdf off Ebay and it’s got what seems to be fairly good electric diagnosis procedures. But as I said this is not my strong point.

    I started at the headlight. The bulb socket is loose in the housing and the lamp checks with no continuity. No voltage at the plug lead on either high or low beam with the bike running. Switch continuity checks out properly.

    Charging coil resistance is supposed to be between .26 and .34 ohms. My meter kept jumping around but the closest I saw to that value was .7. Not sure if that’s good enough or not.

    I did check the charging voltage at the battery. It supposed to be between 6.8 and 7.6v at 3000 rpm. I measured about 7.2 so it’s putting out charge at least.
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    I need to print out the whole electrical section and do some more checking and looking at the wiring diagrams. The neutral and oil indicator lights in the cluster do work. The tail and brake lights work. No headlight, turn signals or horn. The high beam indicator light comes on when switching to hi, the bike has to be running for this.
    #32
  13. Dave in Wi

    Dave in Wi Long timer

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    So interesting development. I buttoned everything back together and took it for a spin. Back in the driveway with it running... I’ve got turn signals. The horn *tries* to beep but I just get a little “Tic”. I checked the voltage at the headlight plug and it’s maybe 1, hard to tell. I need to rig a better way to get the leads connected to the plug. So, maybe just poor connections? If that is the problem I’d be tickled.
    #33
  14. Dave in Wi

    Dave in Wi Long timer

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    So no new progress to report. I’ve been sidetracked with a week of vacation, and moving the youngest up to their apartment at college. I did clean the garage so I have a relatively tidy workspace again.

    And a new development, it’s marking its spot like some damn British bike. Going to have to fix that.

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    #34
  15. cedric

    cedric Been here awhile

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    The headlamp likely runs off an AC circuit while the rest will be powered by a DC circuit off the battery. The tail light may change depending on which key position is used (run vs park)
    #35
  16. Dave in Wi

    Dave in Wi Long timer

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    I’ve been able to do a little more diagnostic work. Checking the voltage output at the headlight connector, I get a fraction of a volt, high or low beam. Going right to the blue wire that supplies power to the whole dimmer switch, I’m only getting about a quarter of a volt maximum. Somehow that’s enough to light up the highbeam indicator light though. So it appears looking at the wiring diagram that my regulator/rectifier may be bad. It appears this part is no longer available. I need to do a little more searching on this and make sure it’s not a bad connection issue. However all the connection I’ve taken apart look pretty good, with no “green crusties”.

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    #36
  17. Dave in Wi

    Dave in Wi Long timer

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    So trying to logically follow the diagnostics to make sure I’m not mis-diagnosing this.

    Charging system checks. Fuse and battery are good. Charging voltage is 7.2 volts which is good. However the charging coil resistance does not check correctly. It’s supposed to be .25-.34 ohms. My meter jumps around but I get .6-.7 ohms pretty consistently. I am not sure if that is good enough, or it indicates a problem. Because it puts out the correct charge voltage I’m inclined to think it’s good.

    Adjustments.jpg


    So on to the lighting system. As I mentioned previously the switch continuity checks good. I’m only getting a fraction of a volt at the blue wire that supplies power to the lights.

    Lighting coil resistance checks at .5-.7 ohms. It’s supposed to be .2-.24. So again I’m not sure if this is off enough to indicate the lighting coil is bad. Since the charging coil resistance checks out a similar amount off, but puts out charge, makes me think the lighting coil is ok.

    Adjustments.jpg

    So it’s either the lighting coil, or the regulator/rectifier. Leaning toward the regulator/ rectifier. If anyone can tell me if the coil resistance numbers I’m getting are close enough I’d appreciate it. What would a bad lighting coil check at?

    Attached Files:

    #37
  18. Dave in Wi

    Dave in Wi Long timer

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    I’ve been thinking about this, how to figure out if it’s the lighting coil or regulator/rectifier that’s bad.

    The manual does not give a procedure for checking the voltage output of the lighting coil. Just the resistance. I’m thinking if I connect the connector referenced in the section below (for checking the lighting coil resistance), start the bike and back-probe the yellow/red and black wires, I should get SOME kind of voltage reading. I’m thinking if it’s 7v or greater the lighting coil is probably good and it’s the regulator/rectifier. If anyone has some idea what the lighting coil is supposed to put out I’m all ears.

    Adjustments.jpg
    #38
  19. Dave in Wi

    Dave in Wi Long timer

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    So I just did the test that I described above. When revving the bike up I was getting maybe a quarter of a volt at that connector. So if my theory is correct, and this connector is “upstream” of the regulator/rectifier, it seems my lighting coil is bad.

    I know this part (as well as the regulator/rectifier) are no longer available. So I’d have to be searching eBay or other online sources.

    If anyone can verify whether or not my diagnosis is correct, I would appreciate it.
    #39
  20. Dave in Wi

    Dave in Wi Long timer

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    Just to provide a little update here. I joined a Yamaha enduro specific forum to get some input.

    Turns out I was checking the voltage wrong. The lighting coil output is AC but I was checking it on the DC setting on my multimeter. When checking it on the proper setting I’m getting a little over 4 volts. Still not up to spec, but it may be enough.

    I’m going to clean all the connections and the hi/lo switch and see if that helps. Since the headlight is NLA I’ve ordered the light below from Bangkok off EBay. It will be here in November, hopefully it will fit and work well enough to make the bike street-legal. Of course by then it will be too cold here to ride much.

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    #40