Some good ideas there I could defo try running without air filter first and see what happens. I already run it on the highest octane I can get. Yes I do have borescope and will take a look this week.

I will start small and work my way through those ideas thanks very much for the suggestions  

Ok latest update.

I changed where I get my fuel from and put in octane boost which defo makes the bike run better it's much smoother and crisper off the throttle and does not rattle as much.

I have also found out that the only difference between mine and the 18 and 19 bikes they are running a slightly larger piston, interesting.

It seems it is a carb issue when the bike is climbing a long steep bank the fuel is moving to the back of the float bowl causing fuel starvation.

The pro riders put a bigger float bowl on to stop this from happening when they are hitting big steps and the bike is vertical.

So it is something you either live with or put on a bigger float bowl, to be honest for the odd time am climbing a long hill I don't think I need to do it and I certainly will not be hitting any big steeps anytime soon lol.

And I have also been told for the few seconds it rattles it will not damage anything at all.

So I think I have a conclusion to this common issue.

I will now just get out and ride and stop worrying about it.

 

I would still try another carb. If my '16 Factory did that, it would kill me with our steep mountains of solid rock. Good Luck.

There is a common issue with the Keihin on big Betas where if you hold the throttle on full for about 20 seconds the carb starves for fuel. I’ve experienced this on my 2008, 2013 and 2018. Usually only notice it on fast fire roads but it does happen. The Keihin doesn’t have a float valve seat. Just a drilled hole in the carb body which is fine for the use the carb was intended, small bore bikes like the KTM 85. Someday I’ll get around to drilling the valve seat bigger To see if that fixes it.

If you don't want to extend the float bowl you can change the drain bolt for an Jitsie one which is deeper than the standard one so will put more fuel into the bowl.