2 stroke smoke (how to limit?)

you can try and buy clean burning oil . but what ratio are you mixing at? i find 40:1 on my RMX 250 works well. but 32:1 is also a good place to start if you are still new to 2 strokes. you are not wasting your time just feel free to try different oils and different ratios. Heck it took me 5 month to find out the motul 800 racing 2t was the best for my bike set up.

proper jetting will solve your problem

2-stroke smoke

I'm wondering what your plug looks like. Is it black and wet? Maybe you are running too rich? Possibly your crank seals are dried out and leaking. go to:
http://www.eric-gorr.com/twostktech/twotopweb_2t.html#Maintenance and Inspection
http://www.eric-gorr.com/techarticles/sparkplugs.html and compare your plug to the first two pictures. A bike that sits for awhile tends to let the seals dry out (yes, I know this from experience).

When you put everything together did you do a leak down test? Eric Gorr's website talks about doing Crankcase Pressure Testing in the first few paragraphs at the following link:
http://http://www.eric-gorr.com/twostktech/twotopweb_2t.html#Maintenance and Inspection

Never really thought of how to limit the smoke. Make sure your air filter is really clean.. You don't want to lean it out too much because then you can sacrifice your engine just to lessen the smoke a little. This also brings up a good question. Are the 2-stroke oils we use today "smokeless" or is that just a term put on the bottles to calm the enviros??

I know once my bike is up to operating temps, it doesn't hardly give off any smoke at all. I'm running Silkolene Pro2, @ 40:1. Its fully synthetic and is a so-called smokeless oil. All I know that my buddy's 02 KX250 running Maxima 927 Castor smokes like a bandit. One problem probably is jetting, but it also has that "sweet" smell to it.

I Feel Your Pain!

I'm new to this 2-stroke thing as well. I just bought a '91 KX 250 last summer. I had the same problem. The bike would blow massive amounts of smoke and barely run at low rpm. Crack into the powerband & wind it out: no smoke and awesome power. I cleaned the air filter and chased jets around but still didn't find an answer. I would sit here and cram "Leak Down Test" in your face, but I have yet to do that myself. What clued me in to the fact that the right side crank seal was leaking was the disappearance of crank oil. I've heard that due to the change in compression ratio between low and high rpm of 2-strokes, when the right side crank seal leaks, it will run great on top end and not smoke, but run horribly on low end and oil foul plugs. I had to take out a loan to cover my plug replacement costs. ;) If your bike is running horribly on low end, I would suggest a leak down test before I would chase a bunch of jets down.

BTW thanks to some info from our friends at Dirt Rider.Net, I was informed by a guy that has a '92 KX 250 that you have to split the cases to replace the crank seals. I hope you don't have to go that far though!

I'm getting ready to send my engine to Eric Gorr for a total rebuild and another guy told me that Eric is able to bore out the seal housing in order to make further replacements easier.

Good luck! Just tryin' to arm you with some info.