87 250X Rejetting

[250XBanzai]

I own a 1987 250X and it is running great. I finnaly decided to get a few more horsepower and I just bought a FMF Power Core 4 and a K&N Filter. I'm planning to run the K&N Filter with the stock air box with cover. Does anyone know the recommended jetting for this set up? Any inputs would be greatly appreciated. Thanks

[jjthekj]

What is your current jetting?

[250XBanzai]

I'm currently running factory settings:
#125 Main Jet
#35 Slow Jet
Jet Needle @ 3rd groove
Pilot screw @ 2-1/2 turns out

[jjthekj]

Try a 38 pilot and a 135 main. Some shops will allow you to exchange your existing jets for different sizes. Or allow you to return the ones you can't use. Some might say to change your clip position right away while you have the carb off but I prefer to make one move at a time and gauge it's impact. Start with the jets. Stay 2-1/2 turns.

[250XBanzai]

My dealer's mechanic just told me that it is pretty much useless to change the main jet if I don't change the needle too. Is he right?:confused:

[rap169]

i ran mine wiht an exhaust and a uni with the air box lid off and it was a 135 main and i think i richened the needle. With the lid on, id say 132. Try the main first and ride it. If you notice any bog or hesitation in the midrange, then adjust the needle