Blown head gasket while running in?
I've been running in a little KH100 after doing the top-end on it. I'm a mechanical chump but I'm trying to learn without breaking the little thing or losing my mind. It's pretty worn and tired and it definitely needed the top end - plenty of blow-by.
The running in had been going pretty much to plan apart from a definite tank cap venting issue - pressure heard when releasing cap, poor/no fuel flow when the tank was on normal but that was temporarily rectified by riding it with a loose cap with no issue.
I'm about 120-150kms into the running in and up until the last couple of rides it has been smooth. The last couple did seem a bit rougher, like it was struggling, but I thought it might have been part of the process. Today I took it for two runs: one 24km run and another short run of about 6-7k round trip. It was a warmer day so I was wary of it getting too hot and kept feeling the cylinder. It was hot to the touch but no hotter than it has been before without problems.
On the 2nd ride a curious thing happened. It stopped on me while I was coming up through 2nd, it just stopped running, so I pulled in the clutch immediately (by reflex I suppose) and the engine came straight back to life and revved up (my throttle was still in the same posi) quite high and then it STOPPED and I rolled to the side of the road. It sounded like an animal screaming as it was being murdered. I thought "I have really messed it up".
It immediately started fine but I thought I'd leave it off and let it cool, nursed it the few k's home but it felt a little 'weak' I suppose. I took the head off to inspect the damage. The bore looked good, there was one short line down the barrel but with a fingernail it didn't feel like anything at all, completely smooth but I was more alarmed by what I found first. The head gasket, a new copper one from the rebuild, and the underside of the head had some brownish gunk over it that I immediately thought was fuel/oil but then I thought it could have been permatex that I used on the exhaust gasket.
Either way, this is a blown or leaky gasket, yes? Can someone help out a chump in the deep end with some advice of what to do from here? Also, perhaps some likely causes. What have I done wrong here?