gamecube viper chip and multi disc games problem

edit - really sorry guys but after messing for what seemed a long time and then thinking it would be a good idea to ask on here i changed some settings randomly just after posting and multi disc game swapping started working. not sure what was preventing it but i succesfully swapped killer 7 and it was the first time the drive would spin back up after opening and closing the lid so ignore the question below

i have a gamecube with viper chip and it still has the same cobra bios on it from when i purchased it which is v1.2.
now according to the info about cobra bios v1.2 release multi disc game support is listed as a new feature, and i don't mean a disc with multiple games on it i mean games on more than one disc, ie metal gear twin snakes.
the issue i'm having is i can't get multi disc games to swap, the disc stops spi9nning when i open the lid but when i insert game disc 2 nothing happens.
surely when the info says multi disc games now supported they were saying that games on more than one disc can be played in revision v1.2 cos that is how it is worded.
some games which have no save point at the swap point are unplayable if this feature is not working, i'm thinking maybe i need to change something in the setting menu to allow multi disc games to play but i can't get it working after trying different settings.
because this is an old system i can't find much info about this issue and certainly no tip about the right settings.