09 300 advice needed

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Hi Guys
Ive recently bought an 09 EC which is/was a 250 and that's what it was advertised as, I removed head to adjust squish and found it to be a 300, the seller didn't even know ?
So, Ive done squish and now need to sort the carburation out, I'm used to the older N style needles and have a few, the best Ive got it running is, 38P R1368G in 3rd and 168 main.
Its not perfect as it idles ok but feels rich right off bottom, clears in the mid and screams topend, wideopen plugchop delivers a nice tan tip.
Most of my riding will be tight woods and trails, no roadwork or mx and I'm out here in the UK, after 10mins tight 2nd gear woods works (all part throttle 0>1/3rd) and entering fireroad the bike take a few seconds to clearout and smokes heavily, as it clears it normally ends up in a huge wheelie

I have tried the R14** needles but they load up to quickly, I have no knowledge of these newer codes and no items to try. All of my limited knowledge is with 125mx racing back in the day so I have nothing lean enough in my needle selection

I plan to purchase a few needles to try, which needles should be on my shopping list ?

Regards

Chris