88 YZ250 Weak Spark - Need Ideas

I have an 88 YZ250 and it has a weak spark. She's almost impossible to kick start, and I have to clutch start it each time, usually by being towed. Once running, she goes great, runs a little lean but has plenty of power and plenty of speed, however she doesn't want to idle. Looking at the plug, it has a really weak spark and I have to kick the engine pretty fast to produce one. Even if I remove the plug cap the spark is still weak, only jumping about 1-2mm. I have changed the spark plug but it didn't make a difference. The spark plug cap has 5k resistance, so it's not that. I have checked the resistance in the stator coil and the ignition coil, and they all have a reading of under 10% above whats in the manual, a little hight but not enough to cause concern, and no closed or open circuits. All wiring is good and connections are clean. Today I pulled apart the carbie and cleaned her out but it didn't make a difference (was hoping that maybe a blocked jet could be the problem). The only thing left is the CDI unit. Is there a way to test these, or should I take the plunge and buy a new one and hope for the best? Also what about timing? The bike runs great when runing so I'm guessing the timing is OK. I'm pretty much out of things to test and out of ideas, apart from throwing money at new parts and hoping for the best. Any suggestions would be great. Thanks in advance.

Oh also (slightly off topic) I've been told to run the bike at a 40:1 mix, but the manual says 25:1. What do you guys think???