Unlike a belt (which my Kingfisher uses) the chain should probably have a bit of slack, kind of like a well adjusted bicycle chain. Sounds like the FEC750 could use an adjustment roller (kind of like an idler pully) to allow fine tuning. I'd give CookShack a call.
Southern Brethren BBQ Competition Team
"It's all about getting paid!" - Myron Mixon
"I love being hated in my hometown!" - David Hair
KingFisher Gator Rotisserie cooker, WSM, Stainless 5 burner with IR gas grill, Turkey Fryer, Weber JD Commemorative grill, slightly used Bandera chamber for future use as a cold smoker, Masterbuilt 40" insulated ELECTRIC smoker