Need Flat Track Advise - RD250 & DT360 - Repost

I posted this in the Old's Cool - 2 Smokers section, but I think I can get more help here.

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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.

Back in the 70's the Champion framed Yamaha Twins used the road racer motors like the TD2 and TD3. The RD 250 will be problematic to get any power out of IMHO.

I am not familiar with that engine. The microfiche does not should reeds, is that correct? Are they the same series as the Bonanza and Catalina (I had one of each)? Were the TDs revised, and became the TZ?

No reeds, piston port.

http://en.wikipedia.org/wiki/Yamaha_TD2

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?

That's odd,I used to race shorttrack and halfmiles and quarter miles back in the day,mid 70's into the early 80's till flattrack died here.

On a halfmile the twins always smoked all comers,usually some combination of RD/aircooled roadrace parts Yamahas. Granted a person would have to know how to build and ride a twin but they are FAST.

Randy Mamola (as a kid) used to show up with 3 bikes,a mechanic or two,and his dad. 3 bikes that matched perfectly and done up to a T.
His Yamaha twin was a rocket,as were all of the expert/pro class twins.

Those twins made the neatest sound flying down the straights and lighting it up off the corners,I suppose a 360 single would be simpler,they always sounded like they were on the verge of blowing up trying to hang with the twins on a half mile.

I agree that a twin will be the cat's meow. But, the biggest thing is lack of seat time on my part. I do not really care to have a twin kill me at my first race

It COULD be more excitement then a normal person could handle,and Im sure a fast one would be maintenance intensive. A 360 could be a 1/4 mile bike,shorttrack bike,and also ride half miles. Twin would be mile or half mile,but would make all sorts of cool sounds. Starting with a DT360 is maybe not the best platform for going fast. The rare 1974 YZ360 engine always looked fast at our local shorttrack,guys yanked the engines and stuck em in Champion frames and they flew!

There is also an issue with trying to find a Champion frame for a two smoke twin. If I can't find a frame, the engine does me no good. A two smoke single frame is a dome a dozen, for the most part.

Don't get me wrong, the twin is what I would like, but I need to work up to it, ability wise.

I have been dreaming about this very bike for a few years now. What is all going on here? I think it is a stock frame early DT, with Astro 'glass.

I had a coworker send me an ad for a '75 RD250 today. I called my coworker a bunch of names for that. 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.

So you were wondering about an RD 250/350 frame?

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<HR align=left color=purple SIZE=1 width="100%"> <TABLE width="100%" border=0> <TBODY> <TR> <TD class=productlistingtext colSpan=2>Frame for Yamaha 250 or 350 Twin (1970 and up) - $1,650</TD></TR> <TR> <TD vAlign=top width=165> </TD></TR></TBODY></TABLE>
Cheney Engineering.
Check them out a guy I know is having them build a frame for his Kawi 650.

I know all about Jerry, he is here in Iowa too. He makes great frames, and has been at it for a hundred years. In fact, quite a few of the local guys run Jerry's frames.

But, I am a cheap ass, and I am a FT virgin. So, I am trying to get by on the cheap, so I can actually get rolling before I break the bank. After some time, I will get serious, and buy newer hardware.

Too bad I sold off all my RD350 road race parts. You might've found things like the CalFab swingarm useful.

The RD250 will work fine. Find yourself a set of RD350 pipes, and I think they bolt right on. I forget the 250 carb size, but the stock 350 carbs were 28mm. Running 32mm on a 350 really woke it up with some mild porting. Any of the road race porting should work well for you and is easy to do.

What do you want, torque or hp? If you want hp, go with bigger carbs. If you want torque, stick to 28-30mm.

You may need to slice/dice the expansion chambers to both exit on the right side or you'll be dragging the left silencer.

The RD400 swingarm is longer if you want that. 250/350 wheels will work on it, but you'll need to make a spacer for the right side to hold the axle.

Get a magneto system so you can ditch the batter. I hate PVLs, and would not recommend them. Their timing curve is all wrong, and they're expensive.

There's an expansion chamber company in texas that makes flat track pipes... forget their name. Not Jemco.. there's another one.

Thank you!!

Should have kept the TT/XT/SR junk and thrown something together. I've ridden 'em in stock frames, modified stock frames assorted purpose built FT frames in a hunert different engine configurations (serious race prepped 540s to worn out stock junk) we don't want to talk about the variety of tires and swing arms we've thrown at 'em Can't beat 'em as far as "BANG FOR THE BUCK"!!! They make great race or practice bikes... I'm A LOT FASTER on my '77YZ250 Trackmaster after some semi serious practice on a Stock framed, stock motor, GOOD suspension and a custom built swingarm TT500.

I still have a pile o' junk in the garage. And, I have thought about putting it together many times in the past six months. I am just being a cheap ass right now. I'd rather throw $600 at my Triumph for suspension, instead of 'glass or wheels and tires for the XT.

What kind of Triumph?

New junk.

'07 America

I built several TD1-C's and TD2 flattrack bikes in the early to mid 70's at Lynn's in Des Moines.
We used Champions and Trackmasters. Several where outstanding.
I'm pretty sure there is one of them (maybe the best) in Ottumwa.
It's a Champion TD2 built for Mark Oswald. Nice Bike!
I have talked to the man who owns it. Might still have his name.
If you can buy a Chenney Frame for $1650 you should!
The Twins are not as easy to ride as a single or maintain. But when they are right, they are hard to beat! They sound amazing!
I have considerable time with them and would like to hear your progress.
Wayne