What is the most common cause for smoke out of the exhaust.
I know that some is expected in a 2 stroke but what is the most common cause. Carbs, low compressions, etc?

Second, out of the 4 atv's I have, 2 of them require me to hold the throttle a little to get them to start. Is this another carb or compression issue? I am finding that I am dumping a pile of money into one getting one to run and trying to get a course of action for the others established.

 

If they're all Polaris atv's the first thing I'd check is that you have 1/8" slack at the thumb throttle lever. If you don't this could be the reason if the etc switch contacts are touching,plus smoking on a two stroke is normal,not on a four stroke. If it's white smoke it's usually oil,black smoke excess fuel,in most cases.You have to start at the basics on all machines. Compression check,good spark,good fuel supply and then any carb problem.

 

If you're leaking antifreeze that will smoke too.

 

A badly tuned two-stroke will smoke a lot worse. Especially from idle to 1/4 throttle, they seem to be a liitle rich in that area. On the 400 polaris. On a two-stroke motocross bike, excessive spooge as they call it indicates you are a long ways on the rich side.
I don't notice as much spooge on my piped 400, as I do on my cr 250. when I'm running rich. I tune the low end by how much smoke I'm getting, the response of the engine and the spark plug color.

I'm referring to air fuel mixture not the oil ratio. The amount of oil will change the smoke. But two engines the same, same ratio of oil. If one has richer jetting, it will smoke more.