Ongoing product design has been defined as a complex problem solving task that is central for the development of new products. Despite its importance, existing work has mostly focused on studying how designers' creativity at the initial stages of design influences the development of radical innovations. However, the role of non-creativity related mechanisms at later stages is still not well understood. Our contribution is to analyze how motivational factors influence non-creative tasks in ongoing incremental design processes. We use an agent based simulation model in which designers improve an existing product by making design modifications based on customers' feedback on product attributes. Drawing on regulatory focus theory, we argue that designers' motivations (promotion focus vs prevention focus) influence the way they search for solutions. We find that, in complex tasks, customer feedback acts as a situational factor that biases designers' decisions, making promotion focused problem-solving more effective than prevention-focused one.