I think you may need to put more than one measure of coffee into the percolator. I use a fairly small percolator.....two cups, but I put almost three measures of coffee into it.....I like it strong and black! I use mainly Taylors of Harrogate ...buy it in Asda.I like their Lazy Sunday especially. I am also using Asda own Extra Special Columbian Fairtrade coffee. It is labelled medium 3 and you can use it in most coffee machines.
hope you find one you like .Im awfully fussy about coffee!!
Grace x