i have a suzuki eiger 4x4 400 quadmatic above tickover it runs ok!
when ticking over its blowing black smoke out the exhaust which normally means over fueling. carb has been stripped countless times,fitted new float and needle.
still no better.the carb is standard far as i know. any ideas welcome.

 

I just had the same problem with my 08 king quad 400 they changed the spark plug to a CR7E its a hotter plug try that its a 5 dollar fix..

 

Have you tried to rejet it?