1974 yamaha dt360 carb

Discussion in '2 smokers' started by Kevin 007, Dec 26, 2010.

  1. Kevin 007

    Kevin 007 Adventurer

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    I don't know how to adjust the needle position.
    #21
  2. stainlesscycle

    stainlesscycle Long timer

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    remove carb top. take slide out.
    remove throttle cable from slide.
    remove spring, remove retainer plate (may or may not have one - depends on carb model)

    push needle out of slide from the bottom.
    there's a clip on the needle.

    which position is it in? needle has either 3,4, or 5 grooves in it. moving the clip UP lowers the needle and leans it out. moving the clip DOWN raises the needle a richens it.

    here's a pic of a needle in position 4 - the richest position on this particular needle.

    you mention it has problems at 1/8-1/4 throttle ? that's either pilot jet or needle positon/taper USUALLY. it could be airscrew too....

    you're in canada. it's probably cold there :) i'm betting richening up the pilot one step, and maybe raising the needle up a notch will compensate for the cold. but it may be too rich when the temperature increases. you say it runs great a wot? with how cold it is it may be slightly lean on the main too. don't forget 2 strokes run the best right before they blow up :)

    you need to google '2 stroke jetting' and go through the whole process. keep in mind, that your proper jetting at current temperature will most likely be too rich when the ambient temperatures increase. keep in mind it's really hard to jet over the internet.

    [​IMG]
    #22
  3. Kevin 007

    Kevin 007 Adventurer

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    Another great post Stainless!!
    Ok I know which clip your talking about now...I had no idea that was its function. I will look into that ASAP, probably weekend tho.
    For some reason, I think the clip is on the top notch....

    The plug is always a little on the cark side however.

    When you say "needle position/taper" is that what we are talking about with that clip raising and lowering the needle?

    The pilot jet is new and free of crud. I have fiddled with the air screw..seems to run best when it is turned "out'' about two turns
    #23
  4. Kevin 007

    Kevin 007 Adventurer

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    Hey stainless I I lowered that clip from the top notch, down two notches. And I think that cured it!!!!:clap
    Have not ridden it much just 100yards and back, due to the snow and cold. But if its not cured, its definitely a LOT better!! I will now have to wait till spring until I take it for a good long ride until I know for sure.

    I have one more question on this machine, off topic but it wont take much, dont want to start a new thread for it.
    -I want lower gears. Will it be easier to swap the front sprocket for a smaller one or the rear for a larger one? It has a 45 tooth on the back...seems pretty generic to me. SO im thinking change the front. Good idea?
    #24
  5. stainlesscycle

    stainlesscycle Long timer

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    switching rear to larger is almost always better. significantly longer chain life. what size is the front now - 14?
    #25
  6. baloneyskin daddy

    baloneyskin daddy bikaholic

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    These years of Yamahas really didn't respond well to big carbs . The transfer ports which carry the fuel charge from the lower end to the combustion chamber are very small with not much room for enlargement via porting. Thus they were low revving torque monsters.
    #26
  7. davevv

    davevv One more old rider

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    For gearing changes, either one should work and I don't find a lot of difference in the effort either way. Changing the rear actually allows finer tuning of what you're after though. As a rule of thumb, a one tooth change on the front will be equal to about a three tooth change on the rear as far as the ratios are concerned, so changing the rear allows you to choose smaller steps toward your goal if you so desire.

    The other consideration is that a smaller front sprocket will induce a little bit more wear on the chain. It's not major, but there is a difference.

    Edit: Stainless answered while I was typing.
    #27
  8. Kevin 007

    Kevin 007 Adventurer

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    Ok, I will likely look into a larger rear sproket then. Maybe a 50 tooth. I want to go quite a bit lower than what it is as the bike will be strickly a trail machine now.

    Not sure what the front it. Looks pretty big to me
    #28
  9. Duck_Pilot

    Duck_Pilot Retired Roadracer

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    Now this kinda thing is just where ADV shines brightest. Here's a guy in BC, Canada, looking to buy a carb to replace one that's giving him fits. Then arrives another inmate from across the whole damm continent, in a foreign country even, who helps the troubled man without his having to spend a Canadian Dime!

    Sir Stainless, Iff'n ya ever make it to ride here in Colorado, I'd be honored to buy you a beer! :freaky
    #29
  10. Kevin 007

    Kevin 007 Adventurer

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    And same goes for a stainless adventure to the great white north!
    #30
  11. Kevin 007

    Kevin 007 Adventurer

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    So now that the snow is disappering...I have been riding/tuning the bike a bit.
    I mentioned earlier that I moved the E clip on the carb needle down a couple notches...this is where is runs the best. I tried each notch, and the middle one is where it likes it. I have also played with the air screw each time I switched notches.
    But the problem is still there, not as bad...but still noticable. I also mentioned that the sputter was happening between idle and 1/4 throttle. Well its actually between idle and maybe 1/16 throttle! It happens just as I open the throttle the slightest amount.. But as soon as I open it any further it runs GREAT!!! and idles great to.
    What should I try next? new needle?
    #31
  12. Kevin 007

    Kevin 007 Adventurer

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    And the plug is nice and tan...it was always on the dark side before.
    I am now starting to experiment with Interceptor premix at a 40:1 Mix
    #32
  13. stainlesscycle

    stainlesscycle Long timer

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    usually a stutter that low (does it go guh/guh/guh then recover instantly and rev fine. like it makes a stutter noise (but not a bog/power loss) when you just ride it with throttle barely cracked open?) is USUALLY a pilot/slide transition issue. or maybe slide/needle transition. what's happening is the slide cutaway is too rich compared to the needle and pilot. the only real way to get rid of it is to go with a leaner slide. that might get rid of the stutter, BUT you may suffer powerwise...(i just went through this on a another bike. replaced slide with leaner cutaway, bike reved and sounded awesome on the stand, but under load it bogged out bad - the bike needed the richer slide to make power in that crucial spot.... i would not recommend changing the slide. you can either lean/richen the pilot out 1 step, or richen/lean the needle 1 step. that may fix it (not sure which way you need to go...) or maybe playing with the airscrew a bit more will get rid of it... the problem with any of these fixes is it may affect how it idles, and ultimately how easy it is to start.......


    you really should pick a premix mixture and stick with it. fix jetting with brass, not liquid...
    #33
  14. Kevin 007

    Kevin 007 Adventurer

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    Yes that is exactly what it is doing. NO power loss, just that guh/guh/guh then instant power gain and smoothness as I open the throttle further. And just as you mentioned, when not under load it idles and revs through the range perfectly!
    The jetting is all stock but I will try to find a richer pilot. I think I have the needle set right for the current jetting...or at least its set to where it performs the best.

    Ok, I am going to stick with a 40:1 interceptor mix. I am still afraid to go much leaner than that.
    #34
  15. stainlesscycle

    stainlesscycle Long timer

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    what is happening is the slide cutaway is too rich for the pilot, so the transition is rough.

    if you go richer on the pilot, it may or may not work.... what really needs to happen is the slide cutaway needs to be leaner. which is a pain and kinda pricey for the risk. and when you change slide cutaway, most likely needle position, main jet, and possibly needle will need to change.

    if there is no loss of power, there's no need to mess with it. try lowering the clip (raising the needle) 1 position. it may get rid of it. or turn the airscrew in/out 1/4-1/2 turn...see if that fixes it.
    #35
  16. Kevin 007

    Kevin 007 Adventurer

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    I have tried each position on the needle, then ran the bike through the ranges, started it many times in each position also. It seems to run the best in the middle position. (3 up from the bottom) That is where I left it.

    I have the air screw turned out about 1-1/4 turn...thats where it does the best also.

    Should I go ahead and put a richer pilot in? ....if I can get one that is:rofl
    #36
  17. Kevin 007

    Kevin 007 Adventurer

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    Another thing I would like to mention is that it will still run with the air screw turned in all the way. I have to bump up the idle just a bit of course, but not much.

    The pilot jet says "05"
    #37
  18. Kevin 007

    Kevin 007 Adventurer

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    I guess the pilot jet is a "50" upon further reseach...I must have been reading it upside down.
    Should I move up to a richer pilot?
    #38
  19. Kevin 007

    Kevin 007 Adventurer

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    I adjusted the float hieght. (raised it a little) this seemed to help right off the bat, but still not cured.
    With the float sitting higher, I also tried different needle settings with the E-clip and played with the air screw. Still a bit of a miss at in the same spot...but better.

    Should I try to advance the stator timing a bit and see what happens?
    #39
  20. stainlesscycle

    stainlesscycle Long timer

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    i would try a richer pilot first. if that doesn't work try a leaner one. BUT more importantly - if you shut the airscrew down, the bike should stall out. if it does not, you may have your idle screw in too far or your slide is not going all the way down, and you are completely bypassing the pilot circuit. does this bike idle on it's own for 10-15 seconds at least before it stalls? and at 1000-1500rpm? or do you have the idle screw cranked way in to make it idle?

    if the airscrew has no effect, you are probably bypassing the circuit....when the slide is all the way down and resting on the idle screw, you should just barely see daylight through the bottom of the slide. does the slide clunk down on the idle screw when close the throttle? if it does not the freeplay in the throttle cable may be not enough.
    #40