Hi all,

I want to check that the stator plate is in the correct position for timing on my 1979 dt250, any idea where or what position it should be set at? I dont have a service manual and my bike came stock with CDI not points
cheers Mark

There should be a chisel mark in case.. usually just to the right of straight up... around 1 o'clock. Can be very hard to see. Use a strong flashlight.

Stator plate and circumference of flywheel will also have corresponding marks. Spark is supposed to happen when mark on flywheel aligns with mark on stator.

Not a bad idea to check with timing light, sometimes CDI box or stator goes wonky and CDI fires way out of time.

Be doubly sure to tighten the flywheel 'Fully' or the crank key might suffer.
If the stator has never been off or moved from original possition the marks left by the screws should be good to rely on.
Stator plate 'Might' have one long mark with a short marks either side.
As MarkT says--good to us timing light [strobe] with it running to see what happens.
Are you having an issue with running as unlikely to be CDI related unless someone's been fiddling [umm-not you of course] previous owner.

Thanks for the replies,

Yes the stator does have one longer mark above the smaller ones, so i gather from this yamaha retarded the timing abit because of chance low quality fuel might be used and they are DTs,
Is there any benefit to advancing the timing so the timing is using the bigger mark between the smaller timing marks? Do ITs, MXs,YZs of the same era have the timing in the middle?
I use 98 octane fuel and i know i would have to watch for detonation if i tried advancing 

The long mark at the edge of the stator is the one you use.  The scale is pretty much meaningless.  The spark happens* when the mark at the edge of the stator aligns with the mark on the outer circumference of the flywheel. 

Timing is done with a dial indicator... when piston is correct distance BTDC you put a mark on the crankcase that lines up with the mark on the flywheel.  Then you remove flywheel and rotate stator until mark you just made on case aligns with long mark on stator.

* that's if everything is working correctly...  original CDI's sometimes go wacky and spark advances or retards several degrees.  Not a bad idea to run engine at about 2500 rpm and check mark alignment with a strobe timing light if you suspect an issue.

P.S.  If you used the long center mark in the "scale" for your timing you'd be retarding the timing, not advancing it. 

I think [might be wrong--waiting to be corrected lol] that the short marks are how much it varies throught the revs.
IE for starting it'll be nearer to tdc on the forward mark [to avoid kickback] & imediately go to the long mark 3.2mm then go towards the slightly more advanced mark when moving off then come back to the middle as revs get up a bit.
Only basing that on how timing varied on my "76 YZ250C years ago [small rotor] where timing varied a lot & way over advanced to try & grab back some low end power when its really tuned to be good at middle & high revs.
Then timing came back to the middle & went forward towards retarded at max revs.
Just to be clear i'm not talking instant changes in timing like the earlier pulser which went retard to start then advance & hold.!!
I guess strobing at kick speed with plug out for easy spin could show it. Then strobe it running.
I only just looked at the pic above so now see all the small marks--so i dunno.
Was thinking one stator mark then on the flywheel a Long mark with a Short either side.
Don't take too much from what i'm saying--what 'am' i saying lol.
I guess we're now talking a DT trail bike --but!!

Over the years the charge capacitor in a CDI degrades and the spark gets weaker. If its possible to find a CDI intended for a newer bike, that will fit and work, running will be improved quite a bit.

On Fantics, fitted with Ducati and Dansi CDI systems, its possible to use Ducati CDI's, which are also used on Lambretta and Vespa scooters, and can be found for very little money.

CDI trick eh!!. Just gotta know what they are. Good info thanks.
Must admit i didn't know about capacitors degrading & thought they either go Bang, or don't.

Capacitor is a bit like a battery, and the ability to hold a charge goes down over the years. This will result in the charge capacitor supplying a lower voltage, to the coil, which means a weaker spark.