i have had a mk2 mohair roof and frame fitted to my mk1 but when the roof is up the material seems very slack is there anything that can be done to tighten up the material any advice would be appreciated
That is strange and slightly worrying as I will be doing exactly the same thing on our Eunos next year.
Material slackness happens when the cloth gets wet or may occur if a MK2 style top with glass window fitted to MK1 frame without the extra rear straps required to properly extend the frame bows.
Make sure the material is properly positioned around the frame bows - it may be that the material has moved, velcro come undone, etc and the frame bows are not correctly positioned resulting in material sag.
Perhaps if you add photos of the sag on the outside and in particular a shot of the bow positions on the inside, someone will be able to confirm.
it may be an original hood. Mazda had a problem with them going slack and changed them under warranty