dataview.rowfilter not working

[Guest]

i have this
DataView dv = new DataView(ds.tables[0]);
dv.RowFilter = "Carmake=" + strCars;
dg.datasource = dv;
dg.DataBind();

I get the error"
Can't find column [BMW]
BMW is the strCars value not the column name so why is this not working?
I have another form like this:
DataView dv = new DataView(ds.tables[0]);
dv.RowFilter = "Type= <> 'USED'";
dg.datasource = dv;
dg.DataBind();
and this works

I need the first one to be dynamic because I only want to show the car make
passed to the page and not all the cars