Hey guys, trying to get this '73 MX250 started....

Looking at the timing, with the piston 2.4mm before TDC, the timing marks are shown in the image below. As you can also see though, there is no more adjustment left to rotate the ignition plate so the marks line up. 

I was given the bike as it sits now and asked to get it running, so I'm not even sure if this is the standard ignition for the bike or not. Any help would be much appreciated!

 

 
 

That's a PVL...  I think they were a successor to Motoplat?  Penton Products used to import them. 

Probably does not have a key or keyway in rotor and it's slipped on crank or someone took it off and put it back on in the wrong orientation?

I know Naathing!! & never seen one [but guessing] if the two yellow lines are the firing point--Does it spark. If marks dont line up @ 2.4mm then forget the crank key [which it might not have anyway] & set piston possition & lock up the rotor nut with marks aligned. Looks like a good simple system. Does it go to an external cdi box or straight to the coil.
Why does it have arrows both ways. Can it operate revolving in either direction like for a RH side ignition like YZ125G etc.

ahh so I didn't even realize that this isn't a stock setup! That explains a lot.

Ok, so it's aftermarket. RT325, those are all really good questions. None of which I know the answer to of course...but really good questions! Hopefully someone on here has some experience with these things.

It does indeed reliably spark and goes straight to the ignition coil.

I found these "installation instructions" online somewhere, but all they tell me is that the timing marks should be lined up to form the "axis":

 

Ok sorry i was just asking incase someone knows the answers. But you say it sparks so that's great but next thing is to see if its sparking in the right place. I mean timing as in 2.4 btdc. I'm thinking the best way [ok my way but maybe not best haha] is to strobe it. Or strobe it to see if the yellow marks coincide. If they do then check where the piston is when those lines are inline. If everything is ok--2.4 & lines plus spark then it should run--well in theory from what we know. Need fuel & compression, clean carb & fuel etc. Goodluck.

Can I strobe the timing without it being able to run while just kicking it over?

My old computer is playing up & didn't see you diagram earlier. I just spin anything of mine with a reverse drill to strobe & makes it easy. You'll have to leave the weight plate off to see the lines but will need the nut on there tight somehow for the socket & extension, drill etc to spin it without undoing the nut.

Ok I ended up just drilling/tapping new holes in the backing plate in order to align the magneto correctly (per the directions linked previously). 

you can see in the picture below how the timing marks align perfectly while the piston is at 2.3mm before TDC. the magneto and markings make the "axis" that the directions talked about.

 

It starts! Now that it starts, however, it's got an uncontrolled idle that i'll make a new thread about. 

Thanks everyone!

Here's a pretty good sounding DT250 unless its an MX as sounds like a smal rotor 'no inertia weight' ignition. Not sure who but just showed up on facebook.
www.facebook.com/100002538953140/videos/...535/1754993031553047