The discs are designed to work at their optimum speed, 8x in this case, and reducing the speed will make no difference to the quality of the burn. Also they don’t make machines and discs with 1x in mind so it is unlikely you will be able to burn at that speed anyway.
Make sure you have your firmware and burning software updated, and make sure the discs are clean and your burner is clean inside.
Finally check that antivirus software and any other things that might interupt the burning is swtiched off while you try a disc.
Of course it could just be that the discs are low quality and so nothing you do will give you a good burn.