ok so I saved up and payed out my but for a Mesa Roadster. It was used and I got it from Guitar Center. Looks great..sounds great BUT....I'm running my DL4 into the Series FX loop..and the delays are distorted and "tiny" sounding and the whole overall tone changed. Ive adjusted the FX loop mix..tried different cables and even took it out of my Furman SPB-8 and ran it alone in the effects loop and it still changes the tone and becomes darker sounding and the delays are distorted and kind of crackle. Help??
I would focus on maybe getting new preamp tube(s)

Are you saying you have no issues when the DL4 is taken out of the mix? Have you tried running the delay up front?

Also ask in the Mesa Owners thread on here and possibly the Boogie Boards on Mesa's site.