Spark plug heat range question.

[ericr]

I'm really shocked you are that far from RB's recommended jetting. I'm at 2000ft and run a 152 main and a 38 pilot.

I was really surprised at this too. Honestly I was careful and not hasty, taking my time, researching, following that excellent jetting guide here on KDXrider.net (viewtopic.php?t=1156) and I went up one jet at a time, and it took a long time (15 engine hours) because I wanted to be sure I wasn't being an idiot about jetting. But yeah honestly the carburetor as-delivered from RB Designs was giving me that lean bogging crap all the time, and taking forever to warm up. I also bought an aftermarket air screw from JD Jetting and an aftermarket idle speed screw so I could fiddle without using tools. It came from RB with a 42 pilot and a 152 main, so 50 and 160 is pretty surprising, especially for 3300 ft above sea level. I blame it on the cold weather and probably 50% humidity.

I'm running a 38 pilot too. That 50 sounds way too rich. You might have an induction air leak. Have you done a leak down test?

['03KDX200]

I'm really shocked you are that far from RB's recommended jetting. I'm at 2000ft and run a 152 main and a 38 pilot.

I was really surprised at this too. Honestly I was careful and not hasty, taking my time, researching, following that excellent jetting guide here on KDXrider.net (viewtopic.php?t=1156) and I went up one jet at a time, and it took a long time (15 engine hours) because I wanted to be sure I wasn't being an idiot about jetting. But yeah honestly the carburetor as-delivered from RB Designs was giving me that lean bogging crap all the time, and taking forever to warm up. I also bought an aftermarket air screw from JD Jetting and an aftermarket idle speed screw so I could fiddle without using tools. It came from RB with a 42 pilot and a 152 main, so 50 and 160 is pretty surprising, especially for 3300 ft above sea level. I blame it on the cold weather and probably 50% humidity.

I'm running a 38 pilot too. That 50 sounds way too rich. You might have an induction air leak. Have you done a leak down test?

I haven't done a leakdown test, although I have thought to myself the engine doesn't seem to be sealing all that great, since I can rest my foot on the kickstarter and it doesn't take long for my foot to start sinking down, and softly kick through the stroke. Maybe 20 seconds. It seems like the motor should be sealing better than that since it has just been fully rebuilt, both top end and bottom end. But it's hard for me to say, I'm brand new to 2-strokes as of 15 engine hours ago. If you rest your foot on the kick starter is it just supposed to sit there, rock solid, for a couple minutes before the pressure leaks out? Or does the pressure leak out in like 20 seconds? (I also broke in the new engine properly with many gradual heat cycles, so it's not a problem of the rings not seated properly yet.)

Also if there was air being "inducted" from somewhere, what do you mean by that exactly?

[ericr]

If you feel like you don't have sufficient compression, do a compression test and compare to spec in the manual. By induction leak, I mean a leak between the carb and the intake. I had a substantial leak in the mating between the rubber boot and reed valves that I found doing a leak down test. A leak after your carb can lean your mixture, leading you to think you need richer jetting. It also makes tuning difficult and increases your risk of seizing.