An old yamaha 2 stroker
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An old yamaha 2 stroker

This is a discussion on An old yamaha 2 stroker within the Technical forums, part of the Caferacer.net Forums category; I'm told that this bike has a lot of interchangeability with the r5 and rd models of that time as well (its a '72) I ...

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  1. #1
    DSstroker's Avatar
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    An old yamaha 2 stroker

    I'm told that this bike has a lot of interchangeability with the r5 and rd models of that time as well (its a '72) I was hoping someone could tell me where to find a list of what is inter-changable. Also, is there a way to get clipons for this old beast or will I have to find someone to make them myself. I've got some mechanical skills. Modified an 86 Iroc with my dad a few years back and already got this bike running strong, but still leaking some oil. I don't;however, have any clue as to how to weld a thing myself.
    And one last question: what sprokets, top or low end parts, ect. to get more power and speed out of this lightweight beastie ( I plan on making it a whole lot lighter too.)
    This is a bike that there is no info to find on online. It was only made for a year and then was replaced by the rd250. Thanks for any help you can send my way.

    hmmmmm rd 400 engine/tranny fit in there?

    Sounds like 2 lawnmowers screaming in tandem.

  2. #2
    DSstroker's Avatar
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    now that I think about it. What about rearsets? I am a newbie so be gentle lol.

    Sounds like 2 lawnmowers screaming in tandem.

  3. #3
    Senior Member snorkelfork's Avatar
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    i read your posts twice and for the life of me i can't see where you named what kind of bike you're inquiring about.



    ...connoisseur of slack...

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  5. #4
    DSstroker's Avatar
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    wow, talk about dropping the ball. The bike is:
    1972 Yamaha DS7
    250cc two cylinder, two stroker.

    Sorry about that.

    Sounds like 2 lawnmowers screaming in tandem.

  6. #5
    Senior Member kenessex's Avatar
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    The DS7 was the 250 version of the R5 with a smaller bore. The R5 topend will bolt right on. I think an RD250 or 350 topend will bolt on too. The DS7 is a piston port engine and the RD series went to reed valves. I think the DS/R were a 5 speed trans and the RD went to 6 speed, but not sure whether the RD250/350 were 5 speed and the RD400 was a 6 or what. I think the DS/R was the basis for the TD1 roadracer and the RD series was the basis for the TR roadracer. Whatever the model designations, there was a roadracer version of the DS7.
    If you are wanting to cafe it some, the forkes and brakes from an RD350 or 400 should be close to bolt up on it. Body work should also work pretty easily. I don't know if the frame was almost the same as the RD or not.

    Hope this helps.
    Ken

    AHRMA 412
    Vintage racing - old guys on old bikes

  7. #6
    DSstroker's Avatar
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    Thanks. I just stripped it down to the frame, engine, and back wheel today. Now I just have to figure out if I need to have someone machine me rearsets or if I can buy them somewhere.
    So a few more questions: 1st: I can rebuild the engine myself with a friend, but not bore it out. Since its only a 250 whats the consensus: to bore or not to bore?
    2nd: will the 350cc R5 top end do anything for power?
    3rd: sprocket change for the back? Does anyone know a sprocket that'll fit on this guy that is still made, that will give more top end ( to use the extra power I wanna give it somehow? )
    4th: Clip-ons for a bike? Where to buy them? Rearsets too?
    And lastly: What colors for the little thing? Hope anyone else can help as well.
    I'm sure by tomorrow I'll have more questions too. Ohhh one last thing: is a 3,000 budget for this project reasonable or am I deluding myself? It was buy a used bike or spend the 3g on this, I figured these bikes mean a hell of a lot more than a factory push out. And look a whole hell of a lot cooler than a chopper.

    Sounds like 2 lawnmowers screaming in tandem.

  8. #7
    slave600's Avatar
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    did u get anywhere on the parts for ur bike (250) just wondering. a neighbor has a really rough one (71, 250, 12k miles, lotsa rust, runs off first kick, he mixes oil and fuel so the oiling system may be junked) and i may get it to tinker w/ but don't wanna bite off more than i can chew. thanx

    03 rsv Tuono custom
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    75 cl360 (cafe /guinea pig)

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    Some of the older repair manuals have a "hi performance" section in the back of them. The ones I have show porting maps and expansion chamber dimensions for the oder Yamahas (YG1,YL1 DS6)
    My first bike was a R5 350. That was one awesome bike.
    DG



  10. #9
    Senior Member UngaWunga's Avatar
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    R5s can make more power than a RD350, but the RD350 has a wider powerband due to the reed valves.

    Yes, everything from a 250 and 350 should bolt onto your bike. RD400 is a completely different animal. Crank is different, cases are different( I think), etc...

    Find a R5 350 top end for it. It'll go like stink. You'll have to rejet for the bigger cylinders, and make sure your oil pump is working or your fry the engine. Replace the engine crank seals or you'll start sucking in air or gearbox oil and fry the engine. Set you points properly or you'll fry the engine.

    Did I mention that you can fry the engine?







  11. #10
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    quote:

    Did I mention that you can fry the engine?
    One thing I do with all the 2 strokers that I get is before I get ready to fire it up for the first time, I put premix in the tank and then start it up. That way if your oil pump doesnt work for any reason, you wont fry the engine (Did anybody mention that you can fry the engine?<img src=icon_smile_big.gif border=0 align=middle> ) . I usually run about a tank of premix through it to be sure the oil injection is working fine.
    Yeah, you may foul the plugs, but they are easier to replace than the top end.
    DG


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