Hello, I’ve been working on this DT400 for a couple weeks now trying to get it running after having it sit outside for about 4 or 5 years. Anyways, I rebuilt the top end on it because the lower piston ring was stuck. Gave it new fluids, wouldn’t start the first 6 or 15 times. Then it started and only stayed running for a couple seconds, it did this probably 3 or 4 times. So I check the spark plug and it’s not getting any spark, sometimes it’ll get spark for a while and sometimes it won’t. So I check the stator wires with a multimeter and the brown wire is only getting 500mv. The source coil has 120 ohms and the pickup 90 ohms. So I tried pulling off the flywheel, switching out every coil except the pickup coil because the spare pickup coil I have is junk. The spare source coil I have on there has a 125 ohm reading. Put everything back together, and well I got spark but still like 500mv AC out of the stator and it acts like it wants to start for a fraction of a second but fails to do so. So I’m sitting here scratching my head whether I should get a new stator for it or I’m just completely missing something else. I cleaned all the contacts on the coils and even put a spare flywheel on it. If anyone knows some common issues or could help point me in the right direction I appreciate any help.

 from Salisbury, UK.

The cdi units on these bikes weren't the best or most reliable, specifically the pulsars.

If you are able to, carry out the checks, in sequence, shown in the Service Manual (this should be in the Tech Library on this site) to see where the issue is.

Ah I gotcha, I was not aware of the tech library. I’ll go check that out, I do have a spare cdi unit I can try as well.

Thank you

My rule of thumb with that type of source coil is about 350 ohms so wonder if you swapped out a bad one for a bad one. Also i go for 80 volts AC [160 AC volts "using a peak meter"] on the brown source coil wire. I'll go look at my old workshop manuals incase i;m  wrong again  lol.
 

Well that stuffed all i thought i knew. My Yamaha book say YZ400 for Europe as near as i can get is 120 ohms brown to black [earth]. Think they run the same mag as a Dt400 just without a lighting coil. 90 for the pulser coil too.
What i've started doing lately is to spin it with a good reversible drill with variable speed & takes all the effort out of it. Plug out & away ya go. Can watch the spark easier than kicking or telling your wife [in my case] to turn the back wheel faster lol. Just gotta be careful of the drill trying to twist your wrist. I just cut the top end off a short socket extension to fit in the drill with a socket.

Just been browsing manuals in the technical section & I'm thinking of the later system like off my It490 or Yz490 & 465 which has a slightly smaller stator & flywheel & says 370 ohms on the "84 IT250L brown to black [source] sorry about that!!.

Check all your connections related to ignition for badly crimped plugs or dry solder joints. I've had that before. I recon all joints should be individual not multi or triple plugs as hard to tell if one is loose fitting.

That’s alright man, I appreciate your help. I have checked for bad grounds/ poor connections to the ignition. I will say that the wiring for the lights is all hacked up but the ignition wiring is fine, no battery either but from what I understand the battery is just for the lights. I did take a look in the manual and couldn’t find a diagnostic tree to follow through with my problem. I will also note that it does start only if I am pulling up on the cable for the diaphragm in the carb (throttle cable is also junk) but if I let it go it cuts off. Probably another issue but still doesn’t explain the 500mv out the brown wire. I’ll have to try using a drill like you said. Also if I connect the kill switch at all it gets no spark either direction, so I just left that disconnected for now.

Your meter is almost certainly reading "average" or maybe RMS voltage...  what you probably want is peak voltage.  In any case there aren't any specs and never have been. 

The fact that it starts when you're pulling on cable (not sure what "diaphragm" you're talking about...  nothing like that in carb I can think of) pretty much makes it sound like you might be imagining a fault exists in a good ignition?  Been there, done that myself. 

Yeah I believe now that it’s likely not the stator. The DT400 was gifted to me and I’ve got about 3 years of automotive experience. All I’ve known is fuel injection lol, just getting into this carburetor and 2 stroke game. The issue likely lies with the carb or just my own ignorance. It does run now that I swapped those spare parts on. Before it wasn’t getting any spark, but it was still getting like 500mv when I had set my meter on max voltage reading as I was kicking it over with the plug out. As it stands now I gotta give it throttle in order for it to start and keep it running. I apologize for any inconvenience or confusion, and thank you for the help.