125-200cc Broken reeds on WR144

My bike's been running a little off colour lately. Fouling plugs unless I've been right into it. On Sunday after lending it to my dad to ride some singletrack (slowly) I was cruising along the fireroad at 60km/h in 6th when the bike ran rough, massive bang (not really a backfire, I'm 90% sure it came out the exhaust not the carb) then died. I managed to get the bike to start and idle but anything more than 1% throttle it would die in the arse. Took carb and reeds off to find two petals broken.





Now a few questions.

Would the plug fouling have been caused by a reed on the way out? Or did the lack of spark cause the 'backfire' and reed destruction. Or is it a bit of both. The bike started its plug fouling with no intervention from me btw.

As you can see in the photos there are some bits missing. Is it likely that they would have passed through the engine or are they likely to be stuck where they shouldn't be?

We had the same thing happen. The bike fouled a plug we replaced it about an hour later, big back fire and the bike would barely idle. The reeds had broken and were pushed back towards the air box, also the crank seal had pushed out of the case on the flywheel side. I never found what was the original source of the failure. Replaced the reeds and the crank seal has been ok since.