Thanks for the info! I just looked it up and you were right, I had no clue the ‘70 didn’t come with a decomp.

How do you distinguish a MX head from a stock head? 

Anyhow, I’ve got a tank on its way so I should have the bike running good next weekend!

If it's a JDM, which it likely could be, it may have had a decomp in 1970... As was already said JDM models often got key features the year before the US did.

Here's another thread on a similar JDM model. yamaha-enduros.com/index.php/forums/1968...ifying-rt1-jdm#43318

Note the longer seat than we got in the US and the passenger grab strap on the JDM model at that link...  both were requirements in Japan.

Also note your bike and the other JDM one in the linked thread have a steering lock...  those didn't show up in the US on the RT until the 1973 model year if I remember correctly. 

Hope this is easier to understand. about the image embedding.

Mx head - plugs point slightly forward, where as standard head plugs point backwards.

I tried an MX head on my DT1 once but made it too harsh--squeezed comp[ression too hard & accentuated piston rattle clearance so gave up on that idea. Come to think of it i 'did' run an MX head on my DT2 running on methanol but std porting & went very well with a race chamber & a GYT kit carb or a 360 carb. But was a new DT2 so tight piston clearance not horse & cart clearance like my DT1.

Thanks Markt for the link to that other JDM bike! And thank you Yamayeeha for the info on the MX head. That’s very interesting!

I grabbed my seat pan this evening and checked it with that bike as well as US model RT1’s and I’ve got a longer JDM seat pan!

In 1972 I bolted an MX head (#284) on my RT-1B with no issues. Was a bit harder to kick thru but it did have quite a bit more torque and pulled harder.

The issue with the shifter/foot brake reversal is very odd. Moving the shifter to the right is easy with the correct lever but moving the foot brake lever to the left side requires some type of frame attachment . I believe the '68 DT-1 had provisions for the brake lever swap, ( tabs welded on the lower frame tubes), at least that is what seems where such a lever could be attached. A picture is posted of a right foot brake lever mechanism somewhere in the Forum, as I had asked this question some months ago. What is odd is later year 250/360's had the shifter shaft on both sides, but the frames for these bikes do not have frame tab provisions for attaching a right brake pedal assembly, my RT1B included.

As an aside, I noticed my 1970 CT1B has similar frame tabs like those on the DT-1, maybe to mount a right brake too, but then there is no shifter shaft provision to move the shift lever to the left. Maybe on the CT1 the tabs were intended for a center stand?

TYPO, meant to say ....but the frames for these bikes do not have frame tab provisions for attaching a LEFT brake pedal assembly, my RT1B included....