to the forum.

I may be wrong but others will chime in here soon to correct me and give advice.

I would start with changing that Spark plug, I've been running NGK BR8 and 9s in my bike. Once you have that done it would be beneficial to make sure that you have the Billet thrust washers and RM bearing in the top end, Not really for the jetting issue but its cheap insurance so you will be less likely to tear up your cylinder. While your doing that you can go through this post http://www.suzukiquadracerhq.com/lt250/87-92-lt250r-engine-reliability-guide/

Before you start changing your jetting you want to make sure that everything else on the bike is dialed in, other wise you could be running around in circles for a while. I would also recommend giving the carb a VERY good cleaning, and record the carb settings it currently has.