Assuming you have the stock Gurter carb and air box installed, your four stroke issue could be coming from your choke not coming off all the way.
The choke lever or cable linkage on the back of the carb can often get bent or be rubbing on the rim of the airbox.. With your side covers off, Reach in and pull the choke linkage cable stop out of the choke lever fork so that you can then check for full range of travel of the choke lever ans you can feel that the choke spring is indeed acting on the lever.
When confident you have full travel you can eliminate the choke as cause of this 4 stroke.
If you think the bike is running lean well then you should screww out your main jet from the side of the carb and make certain that it is completely clean.
You do not have to remove your carb to get at the main jet.