Sickly BigRed - any suggestions?

[Hair Bear Bunch]

Some while ago had an issue with gummed up plugs. Moved the needle clip up a notch and seemed to cure it.
Went out a couple of weeks ago and it ran fine but a couple of times it backfired after switching off. Didn't give it much thought.
Went out again on Sunday, and, well, cut a long story short, pranged it.
It rolled right upside down in about 2' of clay mud, did some cosmetic damage (broken fender, bent bars, broken dash ect.), but once upright it fired up and got back to the carpark, about a 20 minute run. After about half an hour of cleaning, scraping and bending, started straight away and went out again, ran for about 2 minutes and spluttered to a stop.
Nothing we did would start it. All it would do is after 4-5 turns of the engine is backfire. Got it home, good spark, stripped and cleaned the carb, moved the needle back to middle notch and still it will only backfire.
Can the ignition timing slip? Could the timing chain shift a tooth?
I'm at a loss on this one, any advice appreciated.
Rob.

[harryredtrike]

very unlikely the timing sliped.i would get a new plug,and pull off carb and clean well,and check out well.make sure float didnt bend or get stuck in a bad position.also check to see if muffler is packed with crud if it went that far in the mud.also put the clip back on the first ring in the carb throttle slide.where you had it running good

[dz]

Backfiring after its shut off could signify an issue with the valves or timing I think. To be sure, you can check your timing it won't hurt anything. What color is the spark you are getting?

[Hair Bear Bunch]

Thanks for your help, I'm having a day of cleaning up other victims of Sundays incident (clothes, helmet, tools, van, yard, ect.), and I'll have a fresh look tomorrow and see what happens.
No pics unfortunately as the camera was in the tank bag which was upside down with everything else and as it was clean and dry in there I guessed it was the best place for it!
Cheers, Rob.

[Hair Bear Bunch]

Well, put in a fresh plug and it sort of fired. Promising. Gave the carb another good clean and in doing so blew out the little rubber plug that seals one of the jet holes. Saw it go, never saw where it landed! Anyway, made a new one out of a piece of petrol pipe and now it runs. Obvipusly crap in the carb somewhere but all sorted now.
Thanks for your advice.
Rob.