Well most of my experience is with airplane engines but if I was you I would take the engine out,strip and clean every thing.It wouldnt hurt to replace the bearings and they can be found alot cheaper at a bearing shop.Defnitly replace your glow plug and get some fresh juice.All of this might not sound nessery but youll at least know that the engine would be in the best shape its been in three years and trust me a engine can become a proper b!tch if not maintined for a periot that long.