hey martin here to help!
240 main is good, I use a 230
xrsonly uses a 6fj41 needle..use either middle clip or second from bottom( 1 richer) it sounds to me like you are lean because you say you have half power
what is your elevation?
if you need to turn in your idle screw ALL the way in like 3 turns it likely means you are rich
however I know xronly comes with a 12.5 pilot, so that is weird...
you MUST take carb off and see what it comes with..
I like a 15 pilot or 17.5
the 20 pilot I had originally was great for power but had the SAME symptoms you had...the only diff is I ride up to 6000 feet or about 2500m, and I like the 15 better...
I use 2 turns out on the fuel air screw
you MUST not adjust while riding, you have to first get the correct pilot jet then fine tune with fuel scew for different temps and elevations
I like to jet for HOT starts meaning whatever is easier to start when hot and riding...I dont need to start first kick cold, as this usually means using a bigger and richer pilot jet which causes your symptoms
BUT SINCE WE DONT KNOW WHAT PILOT jet you have we dont fully know
plug chops means this
ride at a specifif rpm for at least 30 seconds to a minute without changing RPM
press killswitch and pull clutch at same time
ride to a stop without letting go of clutch lever use break if you want to
then unscrew sparkplug and look at color
3 runs at this same speed will give you a really good read however that takes a lot of time and effort
good luck man
I love myt tm38 flatslide! so you can too