Backfire cracked case

in my experience when things are a bit rich that can encourage the talk back. possibly explains why it will happen a few times in a row for you.
my 250 bikes never kick back, unless ive wrecked and things are flooding a tad. bigbores the kick backs are occasional but soft. after dialing in the carb better on the last 430 it never kicks anymore so i really its a combo of jetting and timing.

Ok cool, I do need to tweak both carbs they have a lil spooge at the silencers.

how bad? small amount is normal unless racing imho

The 87 drips a bit the 79 not so much . I'll take a better look tomorrow.

Not seeing a pic of the crack magnesium can be welded been there done that TIG welded.

I do not have a picture handy though I could take one I suppose. The intermediate kickstart shaft pocket in the right case takes stress beyond the elastic limit, that pocket cracks open, a crack goes all the way up to near the serial number flat. To V out and fully repair is beyond what I would attempt with my equipment and eyesight. It possibly could be repaired maybe in a heated chamber full of argon but those guys are working on aircraft stuff and surely that pays more. The have ways to inspect the repair. That case side in my experience is less likely to have the swingarm insert problems being discussed lately and there also can be problems in the area of the drive sprocket bearing pocket on the other side. Ideally one does not want to mix and match case halves. It isn't like fixing a clutch cover the shift lever poked a hole in during a crash. This alloy of magnesium has impurities come out as it is tig welded as you most likely have experienced. It is designed to be cast and I assume without exceeding air pollution limits.