You will know when the secondaries aren't opening up, the car will feel like you are hauling a trunk full of bricks. It will just make noise and accelerate slow. First thing to look at are electrical problems. Make sure all the plugs and wires are good. Combustion chamber pressures are higher in higher gears so the plugs need more voltage to jump the gap. After that you will need to check fuel pressure. I make it a habit to look over the electrical side first before jacking with the fuel system.
