Stay away from the n1ef needle (stock) or anything similar. Don't even go there.
Start with yamaha yz250 or suzuki rm250 jetting as baseline - as jim cook noted above.
Be sure to go richer on pilot (42-48) and reset the idle (turn it down to get slide back down to where it should be...) 178-ish on main - depending on your fuel - varies a little from country to country... I would start with a 45 pilot and a 178 main.
Getting the proper needle and proper setting of idle and air screw is key to have good idle - good bottom and smooth transition through mid without having a "burble then hit".
Note that this carb can have air screw "out" at 2 to 2 1/2 turns.
Your air screw should have some effect when you turn it - if it doesn't the idle is turned up too high or needle too rich and it is "pulling over" - e.g. fuel from pilot circuit is being bypassed and most air fuel coming through slide and needle jet.
This is typically the condition that it comes in stock - too rich needle - drives person to lean out pilot to 38 and then crank in idle until it is coil bound... Doesn't start easily - doesn't idle, doesn't transition from bottom to mid well. Poor fuel mileage.... And the jetting is too dependent on atmospheric conditions - e.g. you might think you have it dialed in one day and then you go out another day and it isn't quite right again.... So if you see someone say the stock jetting with the n1ef needle works for them - it might work - but that person is threading the needle...
If a person has trouble getting things working with one of the "recommended needles", it is typically because they have not richened up their pilot or they haven't reset their idle and air screws properly. The needle jet can also become worn and "oval-ed" - making the bike difficult to "dial in".
jeff
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