Please tell me if the carbs are interchangble, i have a .40 but i need a new carb, can i use the one off a .46?

I have no idea about their interchangability. You could try looking at the Horizon Hobby site to see if the two engines use the same size carb. Another choice would be to go with a Perry carb. Here's their site: http://www.perrypumps.com/prod01.htm . I didn't see MDS listed, but they give enough details about their models that you should be able to find one that's close to the dimensions of the carb you've got.

I have an mds .40 as well. I know the mufflers are interchangable so I would assume the carbs are but you still might want to check it out.

I used a Super Tigre 45 carb on an MDS 40. It worked much better than the MDS which is basically junk and the main reason Horizon dropped the MDS line. I think the same application will work on the 46, most all engine makers use the same carb on 40-46 applications as I recall? Look for a dead ST or try an MVVS carb....use the MVVS support site and one of the guys can help I am sure. The MVVS carb is less expensive than the ST and much better in my opinion.

thanks man