250-500cc Wr250 Issues

I need some advice on an issue I’m having with my 09 wr250. I’ll start from the top.

When I got it it seemed to be running very rich, lots of splurge down exhaust wouldn’t idle, spluttering and not Revving up. I started with jetting but didn’t have much luck. I then went through systematically checking everything.
New exhaust end can cleaned and packed. New air filter, new plug. Cleaned power valve checked it was working.
Had a new top end 10 hours ago and compression feels good and strong.

Book says jetting should be
Size 60 needle
35 pilot
400 main
4 slide

It came with
60 needle
35 pilot
460 main
3 slide.

I changed main to 400 and bought a 4 slide. Very little change to fueling and bike wouldn’t idle. I put a 61 needle and a 20 pilot and the bike is now rideable and will idle (I changed jets slowly and tried them but this is where I ended up) Still some splurge but wouldn’t Rev up into power band.

I was thinking maybe my crank seals have gone but I’m not losing gear oil and it doesn’t smell like gear oil in the exhaust.

I thought maybe I should start from beginning again so set all jetting back to standard and bike is so rich it is unrideable, won’t idle smokes and won’t Rev up. I went complete opposite and leaned it as much as I could and bike idles and pulls, it then revved up properly but not on WOT(main jet still 400) but it revs up at half throttle.

My question is, is this just a jetting issue and if so why is it so far from factory? Should I keep leaning it out?
Or is there something I’m missing?

After a ride now the plug is still quite black and wet and I still have a bit of exhaust splurge. I live around sea level.
Sorry for long post just a lot to explain.

I now plan to buy some leaner main jets and see if I can get WOT working correctly.

Thanks in advance

Thanks for the reply!
That’s exactly my thinking, something else must be going on but I’m out of things to try.
I’ve changed the fuel needle and seat and tested it to make sure and replaced the jet block gasket to the updated one. Float height checked and rechecked. I thoroughly overhauled the carb as I thought maybe that was my issue. Thought maybe choke was leaking fuel through but it all seems to be working as it should. Checked Reed valve and looks fine, no cracks and seals as it should, had it checked by a mechanic.
Thinking maybe a leak down test next? Last think I can think of. Trying to get hold of a number of a mechanic who knows Mx bikes and two stroke. Should the jetting be this out from what the book says?

Hmmmm in

Hmmm interesting, I did think maybe it’s a carb issue but something that you can’t change.
Mines a tmx 38 flat slide so an older one. Hard to find but maybe I’ll try get one. I know some people put lectrons on them but don’t want to shell out 500 quid. Thanks

Hi
Sounds like you have some issues the jetting shouldn’t be that far off, seems that your engine isn’t burning hot enough to burn all the fuel oil mixture
Are you running a standard pipe and silencer or aftermarket?
Are you over oiling your air filter?
What base gasket you running?
What the squish?