MX250A - intermittant spark.

[Nathan S]

So the newly finished MX was showing a lot of promise at HBBB - until it seemed to run out of spark.
I stopped the bike to rejet, and it wouldn't restart due to having no/very weak spark at the plug.

The weird thing is that sometimes the spark is good - I went to try to fault-find tonight, and its got a fat blue spark now.  ....
It does not seem to be temperature related.

What we've tried:
Several spark plugs (both new and used);
Rechecking all connections;
Re-attaching the spark plug cap to the coil lead;
Checking the coil earth;
Disconnecting the kill-switch;
Cleaning out inside the stator cover (it was clean anyhow).

I don't have any spare stators or CDI boxes of this type, so I can't simply mix and match bits to try to find the drama.

Any test procedures/hints to help find the drama? At this stage, I'm looking seriously at stealing the IT ignition from my DT1 and giving the pre-70 class a miss  :'(

[TT5 Matt]

you say its not heat related but wouldnt a bike on full noise than chopped before the latant  heat had time to disapate cause heat soaking into the stator thus exspanding a slightly dudd coil to open circuit?same with the ht coils,times of taken complete ignition systems into steve at betta bikes for testing the first thing he does is put everything into the kilm to preheat the system for testing with a stationary motor powered ignition test rig maybe the kitchen oven would help with that test if the mrs doesnt object

[Nathan S]

you say its not heat related but wouldnt a bike on full noise than chopped before the latant  heat had time to disapate cause heat soaking into the stator thus exspanding a slightly dudd coil to open circuit?same with the ht coils,times of taken complete ignition systems into steve at betta bikes for testing the first thing he does is put everything into the kilm to preheat the system for testing with a stationary motor powered ignition test rig maybe the kitchen oven would help with that test if the mrs doesnt object

It wasn't given a plug chop.

The bike did a lap of the Vinduro course, was parked for about 15 minutes, and then I did about five ~ ten laps of the MX track before I finally convinced myself that yes, it really did need a larger main jet. There's no way it got hotter while parked, than it was when I left the track.

It didnt miss a beat on anytime it was being ridden.

[Tim754]

Poltergeists. (Being the type of Gremlin that are specific to electrical/electronic devices or circuitry)       Nathan what system are you running standard or a hybrid? Tim754

[Nathan S]

Poltergeists. (Being the type of Gremlin that are specific to electrical/electronic devices or circuitry)       Nathan what system are you running standard or a hybrid? Tim754

100% standard MX250A ignition.

 

[Tim754]

Damn!! that just killed my idea.    Um flywheel key broken worn or distorted? been known to happen.

[Freakshow]

The black boxes and coils have issue similar to what you discribe, id swap them out, im prity sure its the black box,  cause the gel gets loos inside and some parts move about, then fall back into place later on, depending on whick leg your standing on.

Steve warne can fix em up again, buit thats not going to help you right now.

IF i remember tonight and i get time, ill try to pull one off and bring one with me.  you can alos try the one of your YZ125 should be the same, but it will at least show up the fault.

Outside cahnce could also be the coil, i have had them break away inside where the HT lead goes in but as its inside the black core you cant see the copper has fatiged and brkon up.

Other than that i got no idea.    I usually also have a spare coil in my race box so you can try that if you end up taking the bike with you anyway.