Originally Posted by Inane Cathode
The problem is, the only dt400 cdi i can find is $550, and is as old as what is already in the bike. So, that chinese CDI idea, is there a reason an AC powered CDI unit for a two stroke pit bike wouldnt work in the DT? I'm assuming the ignition curves would be different. A few years before and this bike was running points with no ignition advance so it can't be so bad. Just not sure if some random AC CDI box is going to jive with the electronics already on the bike or not, does anyone have any experience with them?
i have chased similar what seems like jetting problems on many early cdi bikes. the ignition sucks at high speed. and things get all wonky. usually the spark is not strong enough to ignite the fuel...so your jetting/plug reads will get all inconsisitent. there is no reason that dt400 shouldn't run decent with stock jetting. if you've been through the carb/no air leaks, and static timing is right, it's usually ignition. give it more than just the fuel from the pilot, and it don't know what to do with it. i bet it runs great on the stand, but sucks trying to pull any load.
to check the exhaust, run a wire pulling snake through it a couple of times. it should not come back without anything on it... i take the pipe off and smack it on the ground a few times, and listen for stuff rattling in there....i don't do this on nice pipes
i swap my 73-75 mx100/125/175 with stators and cdi's from it125/dt175 (1979ish). it costs about $100.00 for everything, and they are super reliable.... i have not investigated your stator setup, but i'm guessing it's the 2 source coil dealio (1 high, 1 low). if it is, the only cheap way is to figure out what late 70's/early 80's yamahas shared the same crank stub. all you really care about is matching a flywheel up (the 2 source coil flywheel will not work with anything but them crappy ass cdis. ) i'm gonna make a wild guess but by about 1978/1979 or so and up dt's/mx/yz/it's all got consistent on their ignitions. there's 4 basic types small bore and big bore, and inner and external rotor. if you start mixing and matching you will see what works. your best bet would be find 1978/1979 dt400 stator/flywheel/cdi. they got real reliable after 1978....
if you give me the measurements of center to center of stator plate mounting bolts, i can at least tell you which stator/flywheel combo will work...the cdi side is easy - any yamaha post 1978 willmost likely work as long as it has at least, a red, orange, black, and white/red - that don't get you lighting, but it does get you running....
you can use the chinese cdi's, as long as you don't care about ignition curve, 99% of them have no curve at all, even though they have a pic of a curve on the cdi :) (careful with that ping eugene.)..
there is a 2 stroke moped cdi i have used in the past, works awesome, has a real timing curve.
either way, none of these cdi's will work with your 2 stage stator.
you want the stators that look like this:
1 lighting coil, 1 source coil, and 1 pickup.