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I ride between 3,000' and 5,000' on the regular. I FINALLY got my jetting working for that elevation range. Running a 38 pilot and a 150 main. Factory needle 3rd clip (still a little fat). Runs great...no fouling. 50:1 full syn. I was fouling in 55F temps with a 42 pilot BTW.

In 2 weeks I have a race at approx 1'600'. I won't have the opportunity to test jetting at that elevation. I may have the chance to do it the day before. I can't afford to foul plugs while in the heat of battle.

So, in a perfect world, you'd rejet. The bottom line is, can I make do with my current setup (with tweaking...pilot screw, tape off airbox opening, etc.) or should I richen it up and go in blind? Looking for experience, advice, tips, etc.

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I wouldn't worry about fouling a plug as you would be getting leaner, not richer, going to a lower elevation. Going lean is much more dangerous to your engine. Yes, I would change jetting. I would go at least one step up on both jets (40pj,152m) and adjust idle mix right before race start after fully warm but that's just me.

I second what SS said with the pilot, main, and air screw. With the needle currently a little rich it might be perfect at the lower elevation.

Ya think going up one size on each should be sufficient?

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If it were mine I would go up one each like he suggested. Check out this jetting guide. It's a 2016 KTM 2 stroke owners manual but it gives a good idea on how much jetting changes from temperature and elevation.

John_S wrote:If it were mine I would go up one each like he suggested. Check out this jetting guide. It's a 2016 KTM 2 stroke owners manual but it gives a good idea on how much jetting changes from temperature and elevation.

Nice. Based on that chart, 1 size up on each should get me close. I just want the bike to come back home healthy! Thanks for your time.

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You're welcome. Let us know how it goes.