Glayne

As feetupfun said, lots of your situation seems normal, your clutch probably needs some new clutch fluid and bleed? some new transmission oil? and some adjustment? Is there a sticking throttle cable? a sticking carb? or a routing issue with your throttle cable?

From that short clip the rattle seems a touch intermittent? Is the master link catching on something? As advised above it certainly sounds chain related, could the wheel be installed any straighter? 9 second video of that is making me want to figure it out!

Any updates?

I wish I could remember what it was with mine? motor magnets need to be 180° from the brushes?

If I was to guess, something needs to spin 180°

This also happened to me on my WR450, I also thought I had it back together the same way it came apart but I had spun the insides 180°. Also as faussy said, wires backwards could certainly do this as well. Definitely messed with my head when it freewheeled backwards!

...And don't rule out the 280! I liked my 250, it was smoother than my 280, and I like my neighbors 300. I can certainly feel the extra 20cc from the 280 to the 300.

New boots are usually the worst, especially MX or ski boots. I had a good experience with new Wulf trials boots. They broke in fast and easy. I definitely prefer used boots for the kids, when they get them they are ready to use!

I could certainly get the itch to ride one of those!

I have always been a Yamaha fan, mixed feelings here for sure! Looks shiny...

Well said turbofurball, Gasgas Pacific in B.C. Canada seems to have any old stock for my EC300 (also known as mototrialswest). It's a few hours north but in my experience great parts, and great to deal with!

I'm not sure what your experience is with trials bikes but they sure don't sound quite like other motorcycles, my 280 2 stroke has quite a pop sound as well and is completely normal. Otherwise I'd be possibly changing out a pilot jet? With a rich pilot circuit I have had very erratic backfiring (on a 4 stroke)

I have a Gasser enduro bike with Keihin carb that does not like this, once I turn the fuel back on the floats will stick and overflow fuel. This is probably just me though, I have good results doing it with yard equipment before storage.

I like my gassers, I get good parts support for them, if money was no object I would likely move on to try something else. I'm still not stranded in the bush, bikes are still much more competent than I.

And at the top of the page I get this "You cannot place a new order from your country (Canada)" I'll try the part # around the Google though. Thanks!