Does OE stays when making duals?

For example I have two swords both at +4, will I get OE duals+4 or is it lost?

No, You loose any +'s on the single swords if you dual them. You will always get +0 duals when creating them.

Thanks, I thought I read that if both weapons are enchanted it stays.

that would be awesome though...get 2 +8 single swords to make a +16 Dual sword ^_^

Nah, the enchants only stay if you exchange a weapon at mammon for a weapon of the same crystal value.

Otherwise (in the case of duals) you could just buy/craft two lower value single swords, OE them at less financial risk (because if one of them breaks you won't lose the whole value of the duals) and when you succeed with the OE, combine them and get much higher value OE'd duals.