Thanks for the replies. Inspected the decompression valve. Seems OK. To confirm, the valve only needs to travel a few millimetres to function correct? I did rebuild it when I did the top end.

Tried kicking over with no throttle, still kicks back.

Guess I'll be checking the timing.

Every old enduro I've taken apart has the tiny little port in the cylinder for the decompressed blocked with carbon. Even a brand new decompression assembly and perfect adjustment won't help a thing if the tiny little hole is plugged. My experience is that the hole is plugged leading into the exhaust port. I've picked at them with tools and wire and the only sure cure is take the cylinder in and have the hole blasted open. Shouldn't be kicking back. They get a bad wrap for the kickback but it's the hole plugged so the factory decomp system is bypassed. Check it out...especially since it runs Good once running. Good luck.

& don't forget the crank key. Especially if it 'was' ok then went crook.

I would love to check the port, but I don't see a way to do it without removing the head? Maybe if I take the exhaust off. I'll try that now.

The timing seems to be a bit off, so I'll get myself a better gauge and really confirm tomorrow.

Have a key on order. Will also be sure to check that.

Thanks!

well, managed to get the valve out, and the port was indeed clogged. Thanks for that insight Pedalcrazy. I'll have to keep an eye on that. Still going to adjust the timing, and hopefully we're good to go. Cheers.

if the port straight into the cylinder was b locked then check the one down to the exhaust outlet. While the valve is out, run something up from the bottom [wire big enough] or put a long drill bit up there [just don't break it off]. If that hole is blocked the valve will have nowhere to bleed to. Might just add, fixing that won't stop kickback but 'will' soften the kick back. I had the decomp on two of mine blocked off & never kicked back but one i'd adapted a cdi mag too so retarded for kicking was inbuilt. Other my current ratbike just has a points mag but no kickback so long as i kick it properly & hard. Mind you it has a raised exhaust port so any kickback might be softened a little. Tis hard on the kick gears though without the decomp working. Could try setting the points at 12 thou just to try, so long as the crank key is good.

I agree with RT325... decompressor just makes the bike slightly easier to kick through, it really does not stop kick back.

It can help prevent the kind of kick back that can happen with a weak stroke-through simply because decompressor makes it easier to give the engine a good spin.

Timing or some other issue is going on if it kicks back regularly... when I was a kid, friend's Dad had an almost new 360 that would try to take your leg off every cold start. Had it "tuned up" by someone and it was just as bad if not worse. He almost got rid of it. Then he took it to the Yamaha dealer and they set the timing with the correct tools and it was fine. He said it had more power too.

Awesome help here everyone.

The bike has always been super easy to kick over, and only started to kick back this season. I've also got an XT500, so I understand the importance of a good kick stroke, so I'm pretty sure I'm good there. I'll check the exhaust port tonight.

I was surprised the port was clogged, as it really hasn't seen a lot of hours.

While I wait for the key to arrive, I'll be timing. I'll see if that helps, and then if it happens again, I'll swap the key.

On to the backfiring.... I'm assuming this is also a condition of timing? Thinking once timing is adjusted, this should clear that up as well?

If not, what else could cause the backfire in the exhaust?