I'm thinking about building a 74 MX250 and using a 74 DT250 motor for a cross country AHRMA race bike. I already have enough 74 MX250 parts, frame, swingarm, seat, pipe, wheels, airbox, gas tank, fenders, side numbers,  missing motor to start build.  I already have two 1973 MX250 that I've built so don't need another MX bike. What you guys think about putting DT250 motor in a MX250 roller. I think a 1975 DT250 motor will also bolt in a 74 MX250 frame, let me know? How about using MX250 pipe with DT250 motor? I have a 74 MX250 cylinder and head, would you install on DT250 bottom end? How about using a  HPI Complete Ignition  to lose flywheel weight? What other parts you think would be good to use and what to look out for during the build. (I'm looking for motor.)

65 views and no discussion, guess most of peeps here don't ride dirt.

Here's mine from back in the day leading an SC500 & RN400, but woulda been short lived haha & second pic probably sums it up, although different day.Here's mine from back in the day leading an SC500 & RN400, but woulda been short lived haha & second pic probably sums it up, although different day.

I'm fairly new here, but my sense is that many of the folks here may be older like me, and used to ride dirt, but are now are restoring older Yamaha Enduros. Not necessarily to ride for competition in the dirt, but just for the joy of it, and to do some trail riding, or just ride around town. Of course, I could be wrong.

If I were younger and looking to build a bike to go racing in the desert right now, I don't think I would use Yamaha Enduro frame. The technology, suspension, and geometry has changed so much over the years, you're never going to keep up with the newer bikes. However, if you just looking to put together a nice bike to have fun out in the desert, that's a different thing altogether. In any case, I don't have any suggestions to offer, but I wish you the best of luck.

EDIT: I didn't know what AHRMA was, and I just looked it up. It's all about racing vintage motorcycles, so I take back a lot of what I wrote. Hopefully someone with a lot more knowledge than me will weigh in and give you an assist!

Many of us pretty much only ride dirt...  and a little pavement to get to the dirt. 

I'm not sure what the reason for putting a DT engine into an MX frame...  A DT250 in that era is not that powerful.  I'd tend towards using the MX engine with a DT (heavy flywheel) ignition. 

You sure have a lot of ideas going around there RUHAPPY. Be good to see the results when these ideas come to completion.

I'm building a cross country bike to ride in AHRMA events from parts I already have, I already have a 74 DT250 motor and 74 MX250 roller. One of my questions is about installing a 74 MX250 cylinder and head on 74 DT250 bottom motor work and improve performance, I already have MX250 cylinder and head. Another question was about changing from stock DT250 ignition to a HPI ignition improve performance for a cross country bike. Thanks Jerry, Augusta GA, 70 yoa still racing MX.

Great photos RT325 and I'm impressed. My first bike was a 74 DT175 and first race bike was a 75 TM100. I stopped riding MX ten years ago and stared back this past year at age 70. I'm a lot slower at 70 yoa but still get that racer feeling.

More power to you Jerry! Still racing MX at 70 years old! You've got a couple years on me, and while I'm still pretty fit, and still working as a self employed radesman, I just get more risk-adverse as I age.

Again, best of luck on the project, and I hope some more folks weigh in to help you with your questions.

It was not clear to me at all that you had a DT engine already....  probably just me...

I would use MX top end, pipe, and heavy (DT) flywheel ignition...

Good luck with the project and let us know how it turns out.