KDX250 Needle question

[nearma12]

I need a leaner needle jet for my '91 KDX250. Currently I have the stock

(R1368H) with the clip on the 2nd leanest position.

Which needle should I go with?

My setup is currently 40/155, #6 Slide. 700ft Elevation, FMF Pipe, Boyesen Power Reeds.

Bike runs a little rich down low and in the mid-range. I am going to change to a 38 pilot also.

Is one size leaner (R1369H) a good choice or maybe two sizes (R1370H)?

Anyone KDX250 guys have a suggestion?

[The Spanky]

I ran a R1370 needle and a 38 pilot. Instead of purchasing a leaner slide, I ground the cutaway 1.25mm larger. I also ran the head gasket from an '88 KX250 for slightly more compression. It was perfect for the N GA mountains.

If you pull the top-end off, you'll find that the drum valves have a "step" where they meet the floor of the port. Grinding this smooth helps add a little bit of over-rev.

[nearma12]

Thanks, I will probably try the R1370H needle and see how it works.

I forgot to mention that I have the Thin 88 KX250 Head Gasket also.

I'm anxious to see how this setup is going to work with a properly jetted carb.

[The Spanky]

My initial modifications (besides the jetting and tossing the airbox lid as far away as I could ? ) were the head gasket, Boyesen two-stage Power Reeds, An FMF Fatty and Powercore silencer, Wiseco Pro Lite (it was 6 grams lighter than stock) and two additional teeth on the rear sprocket. Those mods, combined with the correct jetting, absolutely transformed that engine. It had so much low-end grunt that I would climb hills lugging in second and third that other bikes had to scream up in first and second. As long as you kept the throttle open, even at ridiculously low rpms, the engine would pull and would not stall. The midrange was outstanding, the bike would hang with MX bikes of the day. And it even revved decently on top. You won't be disappointed.

I eventually ended up with head mods and porting, and a titanium rod. That engine was sweet. Powerful, torquey, smooth, and fast.

[nearma12]

Yeah, I really like that motor. It ran strong when properly jetted in stock form. I am really looking forward to getting it out this year with all the mods.