Why is my mower not wanting to engage the blades right?

Why is my mower not wanting to engage the blades right?

2013 cub cadet 1050. When I engage the mower deck it wants to sputter to a stop. If I mess with the throttle a little it will come on and mow perfectly. Sometimes it just does its little sputtering fit and will engage. New belt, spindles, blades, and fuel filter.