I'd say the lumpy feel is caused by one of 3 things, either:

a) the wheel itself has a hop in it that needs to be trued out
b) you aren't stretching the tire onto the rim evenly, ending with lumps
c) the valve isn't centered in the valve hole, causing a lump.

I'd check the true of the wheel, and if that's not the case, pull the tire off and when you glue it back on, really pull on it to stretch the first section onto the rim.