[Asmith]

the bike was running very rich prior to this carb issue,

In my opinion MXA's solution still has it running WAY too rich.

The 2008 CRF 250R was one of the only R's to be jetted horribly out of the box.

The main is WAY TOOOOOO BIG. It's a 188 forchristsakes!!!! It is loading up fat on top.

Knock the main back to a 172 or 175 and you should have much better results.

If you have some off idle bog, swap the leak jet out for a 55.

Set the fuel screw at 1 3/4 to 2 turns.

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Don't sweat it gaines1016, this'll all come together for you. MXA is Motocross Action Magazine, by the way.
My experience with them began this last March. A group of us rented an indoor facility and two guys went along with 250R's, an 06 and an 08, both next to new, the 06 being a 'left-over'.
Both ran very badly, the 08 very weird . The 06 that went along with us had a big-time bog
My sons 08 incidentally had seemed way lean up top and way fat on the bottom.We installed a JD Kit on his and it ran great top to bottom with a 188 main.
Both guys copied what MXA suggested and both bikes just ripped when I saw them next.
Jetting requirements can change according to a lot of things, but it should be noted that the MXA guys race their bikes every weekend for about a year and have a good reputation for knowing what they are talking about too. My 07 450R had a JD needle set-up,and JD recommended a 190 main (from a 180). It somehow was in no way too rich at high rpm somehow. I still don't get that one and certainly welcome opinions.
The main jet is the easiest thing in the world to change. If it was me I'd still copy their settings and go from there. Doug