When blue smokes sit for a long while the crankcase seals can get dry then the seals do not work particularly well.
Remember the cylinder compression is only 1/2 the equation you also need primary compression.
The easy way to diagnose it ( and not particuarly accurate ) is to spray some of your favourite goop down the carb throat, remove the plug and give it a few pulls
When the exhaust blows clean, replace the plug and try again.
If it fires up quickly and feels harder to pull it is a sure sign your seals have dried out.
The harder and proper way to do it is to both a pressure & vacuum test on the crankcase.