I was thinking that a DT400 flywheel could swap into a DT250 (I thought I read that...is that incorrect??), so in my never ending quest to find a functional flywheel I eBayed one. The part numbers matched...F0T01971. They appear to be identical except for one thing...this one didn't have the relief cut around the edge. Is that done to lighten it? Or does it actually need to clearance to fit? My motor is all torn down, so without slapping the crank back in I can't test fit. Measuring the best I can from the case, it looks like there might be about 1/10" clearance. I did take a picture before disassembly, and that area looks tight. If necessary I could get the "new" flywheel turned down. Separately from the F0T0#, the 400 flywheel is marked C2 where the 250 is marked D1.

Hope i'm wrong but 250's were points up to late "70's, "78 i think, where 400's were always cdi. Flywheels probably look much the same from the outside but 250 one will have a cam of course.
Also just having another look at your pics, the flywheel on the left looks like the keyway is more towards the right rivet-- but the right flywheel in the pic looks like the keyway is in the center, equal distance between rivets. Not even sure if it matters & might be just an illusion of the pic angle etc.

What you have is two DT250 flywheels. The entire 400 ignition (CDI) will swap over, not just the flywheel. (The CDI flywheel does not have a points cam inside which is why it won't work on a 250.)

The 400 flywheel has a different number on it. Someone probably converted a 400 to the 250 points system to replace a non-working CDI on the ebay bike you got the flywheel from.

I don't know enough about the bigger bikes to tell you why the rim was turned down... 1974 was a "transition year" with some one-off parts. The 75-76 250 also used the FOTO 1971 flywheel... I have a 1975 250 and don't remember the rim turned down so "maybe" the 74 had a slightly smaller case opening than a 75-76?

The only thing I know for sure about the 250/360/400 ignition swaps is that in 1974 the case opening for the flywheel was made smaller than the earlier bikes... so you can swap an entire ignition (not mix and match parts) from a later bike into an earlier one... but you can't use a 1973 and earlier ignition in a 1974 - on bike...

Aha that does make sense. I had wondered if maybe it had been a swap at some point which led to it being mis-labeled when it was sold. I should have stated originally that the "400" flywheel definitely has a points lobe in it. I wasn't sure if there were some Dt400s that ran points and some cdi...

It looks like this one will work, and if upon reassembly I find that there is a clearance issue, I'll have it turned down a wee bit.

Thanks for the info, guys. Hopefully this ends my flywheel debacle. On to the next debacle!

No help sorry but just found one close to me [when not looking for one lol]. www.trademe.co.nz/motors/motorbikes/part...447e89a1bbc0cc3825db

Oh wow, well thanks for passing it on. Yah, these things seem rare. And is that correct where it says below it was used on the '76 Dt400? So they had cdi in 75, then points, then back to cdi? I swear all these models and ignition types make my head spin! And that flywheel appears to not have the outside edge turned down either, adding to the mystery.

They did not go back and forth between points and CDI any more than some sellers will list a "magic" piston ring set that fits both a 250 and a 400...



Yamaha shared the parts microfiche slides they used back then between similar models (250 and 400 are very similar except for engine size) and the new parts lists made from those old lists can be confusing. Hint: First 3 numbers of part number are the "model code" and can help identify which part fits which model... but not always! Sometimes it needs an expert like Enduronut or DEET to identify the correct part.

P.S. Those rings have a 438 prefix which is a DT250 model code so should be for a DT250... Enduronut is the expert on pistons and rings (and most other things) so if there was a question he would be the man to ask.

A couple of different model code lists are available in the Tech Library.... my favorite is in the "Service Bulletin" section.

Hi Luke, I am in the middle of a flywheel/ CDI / mismatch ! I have a 1977 DT250 which when I purchased it was told it had been fully restored, on the first trip out the flywheel came loose, after re fitting it properly next time out I found the bike won’t rev over 3,500 rpm. The bike is fitted with an aftermarket Rexspeed C.D.I kit. Everything else has been checked out, fuel supply, float height, reed valve, crankshaft seals etc.
I have just returned the CDI kit to have tested, but they are thinking that it may have the wrong flywheel, and it may need a photo 1971, if that is the case is it possible you may have one you would sell ?

Can't help you with the Rex's thing. Several people have had issues. Hopefully Rex's will sort it out for you. Seems resolution is hit and miss from what I've seen... No personal experience myself.

If they meant was a "FOTO1971"... (might be some extra O's in the stamping) that's the number stamped in the 1975 DT250b flywheel (and probably 1976) which sounds odd because the 250's had points and I thought the Rex kits were geared for replacing the problematic 400 CDI's.

I'd wait until you get confirmation from Rex on what exactly model flywheel would work with the stator you sent them.

(Points flywheels can be harder to find because points systems are a great way to fix a bad CDI IMHO. )