Need Flat Track Advise - RD250 & DT360

Discussion in '2 smokers' started by Calkins, Jan 15, 2014.

  1. Calkins

    Calkins On Any Sunday...

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    The past few years I have been slowly trying to get a flat tracker together. I had a TT500, was ready to race (I think), and had an offer to sell. Recently, I bought back my old pile of spare TT/XT parts, thinking I would going to build another one. But, an old family friend of mine wants to help me put a two smoke together. He was a Yamaha mechanic back in the '70's and '80's, and that is what he would like me to build.

    So, this is what I would like to do. There is a "local" series, the Classic Flat Track National Championship Series (http://bikedays.com/id52.html), that has a few half mile races a year. Usually, two are held here in Iowa, Davenport and Knoxville. I want to run the V250/360 class. Back in the day (1973 to 1976) that meant 250cc two stroke twins, 360cc two stroke singles, and 360cc four stroke singles and twins. From what I have seen, the Honda XL350 owns the class. I have not seen many smokers. For me that is great, because I would rather be unique.

    So, what I am questing for is technical information. I would like to put together a RD250 and a DT/RT/YZ360 powered Champion. Which engine/year/model, for each, was/is the hot setup? The reason I am wanting to build both, is because I think it will be harder to find a Champion frame for the RD, so the DT will probably get built first as I find RD parts. Then, the DT will probably get switched to a short tracker or TT bike.
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  2. Calkins

    Calkins On Any Sunday...

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    I talked to a guy that has been racing a Yamaha two stroke twin for the past 15 years, I think that is not the way I should go.

    So, DT360 tune ups. Any advise?
    #2
  3. pdxjim

    pdxjim Two Stroke Terror

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    Go go go!!!
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  4. stainlesscycle

    stainlesscycle Long timer

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    mx360 may work better than dt360.
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  5. Calkins

    Calkins On Any Sunday...

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    There was an old thread on the FT.com about the old 250 and 360 Yamahas. The old boys thought the DT and RT were tuned pretty close to each other, and the MX was a little hotter, and the YZ was a little hotter yet. The MX had a balance shaft in it. If that was removed, the MX would work well. The MX and around '74 on up DT got wider engine cases, that would scrape the ground in the corners.

    This is all here-say from old foggy minds. That is why I started threads, to get some answers.
    #5
  6. buls4evr

    buls4evr No Marks....

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    If you want to be truly "unique" AND FAST, you should be on a Bultaco 360 ASTRO. Torque like a 4 stroke off corners and revs like the Yamaha.Lighter than any of them...... But alas, you seem to be a Yamaha guy.
    #6
  7. Calkins

    Calkins On Any Sunday...

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    Actually, I am into Triumph and Husqvarna.

    I would love an Astro. But, I do not have $5000+ to throw at a toy like that.
    #7
  8. stainlesscycle

    stainlesscycle Long timer

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    i like the astros too, but wouldn't call them unique at a flat track event..
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  9. buls4evr

    buls4evr No Marks....

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    Not "unique" to see the 3 Astros battling 20 Yams and Hondas in the class?And at least 1 of them ends up on the podium:clap. They come off corners much better than an MX360 and have a lot more power than an XL. They are worth that money if you want to win. Ability to pass on corner exit is everything in flatrack.
    #9
  10. Calkins

    Calkins On Any Sunday...

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    Having a Bul is on my wish list. I would like to get some seat time with this Yam 360 deal first. I have a feeling that I have much to learn with riding a two stroke. Heck, I have plenty to learn with just the flat track part of it!
    #10
  11. stainlesscycle

    stainlesscycle Long timer

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    sorry if i was not clear, the only place an astro is not unique is at a flat track event. i.e. it's the only place you would expect to see them. that being said, surely there is more to flat track than the ability to pass on corner exit.. :evil
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  12. buls4evr

    buls4evr No Marks....

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    Sure Stainlesscycle, a lot more to it. But that type of pass is the most solid and certain. Some believe the fastest bike at the end of the strip is best. If that were the case then an RD250 would win. It is seldom the case that a "going in" type of pass sticks as you often go "off line,high", and get passed right back. So a coming off corner pass is most certain because your immediate opponent has no answer for it.
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  13. Calkins

    Calkins On Any Sunday...

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    I had a coworker send me an ad for a '75 RD250 today. I called my coworker a bunch of names for that. :freaky Anywho, it is super cheap, and local. I am going to check it out next weekend.

    What makes the stock frame a pile to flat track? If I could make the stock bike handle well enough to last me a little bit, it would buy me time to find a proper purpose built frame.
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  14. buls4evr

    buls4evr No Marks....

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    Calkins, a stock frame is not rigid enough in the steering head area or the swingarm area. It also has too much rake..... Angle is wrong so it will not "turn in" well. That means you will be on a high wobbly line:eek1, in corners. It is also weighted incorrectly front to back. You want a Champion or Knight frame with Barnes wheels so you can change gearing readily also.Those frames fit a variety of engines that I mentioned. You need to buy,build motor mounts for them and the RD250 ones are probably available on vintage forums.The RD engine has the most HP of all of these engines except the Bul, but it makes it way too late down the straights.Really bad for shorttrack, barely passable for 1/2 mile. 2 expansion chambers are also a nightmare in that environment.Hope this all helps.
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  15. Calkins

    Calkins On Any Sunday...

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    Thank you!!
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  16. Calkins

    Calkins On Any Sunday...

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    Also, half mile is what I would be running.
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  17. Rich B

    Rich B Long timer

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    From reading this thread, it doesn't appear you have much experience on flat track. Some really good riders ended up on their ass trying to ride an RD250 or RD350 on dirt..... :eek1 Some really good riders also went pretty decent, but more ended up on their ass than on the podium.

    The twins, regardless of how well they did on pavement are at best, an evil bitch on the dirt. Narrow power band, wide cases, and limited torque requires a skilled hand on the throttle and quick reactions in trying to keep the beast tamed.

    In the end it is your bike and your ass......:lol3

    If you are starting out, you would be much better finding something you can ride. An RD250 is not ever going to be a beginners bike. The RT1 based bike would be ok, no Bul, but ok. Move beyond that and you are probably going to have a tough time learning to ride.

    You don't have to have a B123 or later Astro to have a Bul. There are some other models that did the job in the day. Look around for a B68 Pursang that is missing a lot of the fiberglass you would remove anyway. Reality is, the M68 was the beginning of the path to the Astro. B90's, B105's, B106's were steps along the way. A relatively complete B90 is on fleaBay right now for a decent price. If my Champion Astro wasn't consuming cash, the B90 would probably be mine. Later Sherpa S or even MK V Pursangs will do the job. Any of them will be easier to ride than the RD250.

    Just my opinion...... :D
    #17
  18. Calkins

    Calkins On Any Sunday...

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    If this RD250 turns out to be a deal, I will buy it and store it. The plan is to build a Yam 360 for now. I have a short track event I would really like to hit in May, if I can get something built. Then, half mile events in June and August.
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  19. Calkins

    Calkins On Any Sunday...

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    Also, I think I am getting terminology confused with the Yam. What is everyone considering early and late engines, also narrow and wide cases?

    Are the early engines up to 1976, and late engines are 1977 and later?

    Are the narrow cases the ones with a four bolt jug, and the wide cases the ones with six bolt jugs?
    #19
  20. stainlesscycle

    stainlesscycle Long timer

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    wide cases in general. i.e. gonna drag cases/shifter in the dirt wide. a single yamaha 360 is PLENTY of bike for short track..... the frame geometry might suck, but it'll definitely go fast enough for any short track event..
    for short track you need enough torque to pull hard to 3rd, and to flip flop between 2nd and 3rd and 4th and stay in the power band. the rd's generally don't have the grunt in the right places. you need a ton of torque at corner exits, that's why the 500 thumpers do so well..
    #20