Snow blower repair?

Just changed the engine and auger belts in my 30+ yr. old snow blower Mdl. #TMO-35268B Montgomery Wards. The idler pulley for the auger belt doesn't push the belt tight enough against the engine pulley to generate much power to throw snow. I changed ALL the springs to new and adjusted them according to the manual. There is still 1/2 to 3/4 slack in the belt after the auger handle is depressed, but I can easily take up that slack if I manually pull the idler pulley onto the belt. I don't want to throw any more parts at it just yet. It has to be something I'm looking past. Any ideas?