After cleaning the carb, fresh gas, new fuel filter, and oil change with filter I started doing the resistance/voltage checks from my shop manual on the stator, pickup coil, voltage regulator, CDI, and ignition coil.

Stator - Everything within range.

Pickup Coil - Resistance within range, cranking AC voltage 0.2, idling 1.0, high rev peak 1.8. My manual says cranking should be atleast 0.5, but values are exactly the same hot or cold.

Voltage Regulator - Resistances within range, failed the test where you hook up 24V and it's supposed to dump it to ground. The battery voltage climbs to 13.5V when running and never goes over when hot, cold, lights off, lights on. From what I understand the ignition system is powered off battery voltage and so as long as battery voltage isn't high, even if the regulator's bad it won't hurt anything.

CDI - Failed almost every resistance test. The values don't change when hot or cold, so I'm not convinced it's a CDI issue yet.

Ignition Coil - Resistances within range, and spark will jump biggest gap my tester can provide ~12mm hot or cold, SM specs 7mm.

Not having found anything conclusive, I hooked up a timing light to check base timing and advance. When cold, base and advance looks good. When hot, timing looks good, but when misbehaving it's obviously sparking a lot slower like it's missing 2 out of 3 times.

I went through the wiring harness front to back, cleaned every connector, checked resistance of every run and connector related to ignition, and reassembled. I found a huge resistance across the fuse by the battery, even though the connections all looked shiny and new. Cleaned and fixed that connection. Rechecked charging voltage and still good.

After all this, the bike starts and runs even nicer than before but only when cold. It still won't rev when hot.

 

I'm thinkin it's a CDI problem. That's what controls your ignition.

 

Nothing from my tests indicates any change in the CDI's resistance values hot or cold, so I'm not sold on that yet. And I think it's an aftermarket CDI, so the resistance values may not apply.

I'm going to try and borrow a CDI from a friend's bike to test.

 

That's a good idea before Ya spend any money on it. I can't think of anything else for it to be unless it's a tuning issue with the carb.

 

Swapped in a factory CDI from a friend's bike. No more rev'ing problems when warm. Noticeably less power and quieter exhaust though.

After some more experimentation I discovered that I can cure the rev'ing issue with my old CDI for several hours by pulling it out of the rubber mount and whacking it on something hard when it starts misbehaving. :lol:

So clearly it's a loose connection in the CDI somewhere, and I'll replace it eventually. Out odf curiousity I checked resistances according to the manual pre and post-whack and no change, kind of frustrating.

 

Well that sounded too easy :lol: