My daughter's 86 Brat GL runs out of gas when it has only used about 4 gallons. The float sinks, so the gauge is not much help. The tank has no obvious dents. Any ideas>

Filter(s), pump?

Fuel pick-up tube has a hole at the 4 gallon level.

Pickup up tube in tank could also be clogged. I've had a problem with gas delivery, and had to hook up a hose so I could blow back into tank. Remember if you do this to remove the gas cap.

Thanks. I am going to change the filter and drop the tank to look at the pick-up. The pump will be next.