The 77 DT250 flywheel recessed down too far on crankshaft causing the crank to not turn at all.  Noted, was not as recessed on stock application which when
tested worked great.  Is a FOTO1971 flywheel.  

 MarkT, I know this is your specialty.  Any ideas?  More to come on why I'm testing later.


 

never had that issue

If and when you get a 250 setup to fit your DT360A then, if needed, I think that DEET might be able to supply a sub harness to link the wiring from the stator, to that on the main harness (I got one from him a few years ago for my own conversion).  

Like the harness idea.   Going to look closer and see if I can figure out why the crank is jamming on stator plate.  

put it on a 2nd engine I have…and same results.  
Spins about half turn then jams.   











 

How did I miss that?     

Pics are from 2 engines:

Engine 1 and 2 had similar clearance problems:




 

I'm not confident FOTO1971 belongs to a 77 DT250D?
 

Ok, that explains a few things. FOTO4274 per service manual and a 1M1 part number.

I recently bought a ignition system that came off of a 1974 DT250A and it has a FOTO1971 flywheel, if you need pictures of the stator or flywheel I can text or email them to you if you PM me your info.

Thanks, Lizeec.

In that case, with the correct DT250 points stator in place, should it not just bolt right on?

The FOTO1971 flywheel is likely correct for the 77 DT250 as is the stator plate with it. I found another bike with exactly the same setup. That combo will work just fine.

I think I figured out why it didn't fit without the above clearancing in green.

The DT360 has 6 cylinder studs. 2 are lateral to the piston and 1 of them is right over the flywheel. Yamaha apparently needed more support for the stud. The DT250 has 4 cylinder studs and has NO BOSS nor stud where a stud would normally be on a DT360.

The DT360 has a FOTO2171 that is MACHINED DOWN on the outer edge several mm (~2.5mm) from the factory for the boss of the cylinder stud. The FOTO1971 DOES NOT have this relief. The 250 didn't need it.

I weighed the 360, 250, and VAPE flywheels. verified 100ml of water close to 100gm, so these weights should be fairly close.

DT360: 1.764 KG (22 GMS less than a 250..LOL probably the removed outer ring for the boss on block)
DT250: 1.786 KG
VAPE: 0.976 KG

A few Outer Diameters: 
Stator Plate:   130 mm
Flywheel 250 : 129.94 mm
Flywheel 360 (outer edge):  127.43 mm

THIS is the reason I am testing the flywheel in the first place. To see if I can dampen some light vibration I'm getting. I pulled crank and had run out adjusted cleaned up as much as possible and even swapped cylinder/piston combo as a test and ptv clearances. This week I look forward to trying the new, heavier flywheel.

The clearance needed was only about 0.010" though I cleared a little more space. not much more. Going to be careful on first crank up.

Part of the goal here was to go back to basics and test the flywheel weight. Points and condensers are easy to get. I have a set from an XR75 that can be bought for < $25 (minor mods and 0.22 vs 0.25uF condenser). I'm sure there are many others. VAPE makes a 2kg flywheel kit, 7345799, but $$.

I'll post up when I get it all tested.

edit: LIzeec.  Thanks, I'll send a PM