This is what I found when cleaning my econo 1, I took the combustion motor out to clean it good and oil it. I looked in the hole and could see the fines under the grate. I took my vac and cleaned it out through the combustion fan hole. It was much easier than removing the grate.
That's the way I do my Keystoker as well, make sure to clean all the plate holes first. I use a brush for a refrigerator cooling fins to loosen everything up while I vacuum, works well, kills two jobs at once & you don't have to reseal the grates.