Get the engine turning freely before doing anything. I'd take the carb off and soak the whole thing in a small cup of methanol or fuel for 20 minutes and make sure the passages are clear of oil residue. Reassemble, change the glow plug, and get after it. If the engine turns over rough and gritty, change the bearings before running it or you'll likely ruin the piston/liner fit and probably the glow plug too.