Jesus never said, "If you had more faith, God would answer your prayers."
Jesus never said, "If you had more faith, God would answer your prayers." He said some things that resemble that line. But he never actually said that God's response to your prayer depended on how much faith you have. To understand what Jesus actually said, we have to look at what we mean when we talk about faith, what we mean when we talk about prayer, and most importantly, can we expect God to answer our prayers?
When we talk about faith, what we mean is trust in Jesus. Not a vague kind of optimism. Not confidence in a particular outcome. Not a careful calculation of the relevant factors and a prediction about the future. When we talk about faith, we mean trust in Jesus.
When we talk about prayer, we mean making a request, confident that the One to whom we pray can answer us. Prayer is not just requests, of course. Prayer is sitting quietly in the presence of God. Prayer is confession of our sins. Prayer is seeking guidance for the living of our days and for recommitting ourselves to God's purpose. But for right now, prayer is bringing our requests to God.
Can we expect God to answer our prayers? It depends. If we have already determined what the answer to our prayer should be, we may decide that God did not answer our prayer. But if we are willing to allow God to decide on the answer he gives, then we may well determine that God has in fact answered our prayer. In this, Jesus is not only our teacher about prayer, he is also our model of how to pray. He made his request to God, but he added, sincerely, "Not my will, but thy will be done."
"If you had more faith, God would answer your prayer?" Not quite. But if we have enough faith, if we trust God and Jesus, then we will accept the answer he gives.