1/8 inch gap is what it calls for in the manual and I always start there and do a little adjusting from there if needed,I have as well as a freind of mine,have had to just send them back in,but the ones that I have now run just as strong as an fx,any day!not dogging o.s. cause I've had them to,but I like the tower engines and think they run great once dialed in,and if your a tower memeber,you get a 4 year waranty!can't beat that. Oh,ya and I bet if you call tower and tell them you lost your manual,they would probaly send you a new one.lol