Weird problem with fuel line
I went for a ride on the weekend and found myself stuck at the side of the road, with a weird problem.
The bike starts fine and runs fine. Then, after about 1/2 hours, after a long downhill, the bike feels like it's running out of petrol, then eventually stops. There is plenty of fuel in the tank. Try to re-start: no luck. For some reason, the fuel switch was set to reserve. It switch it back to normal, then it works fine. I keep going. After another 5 minutes, same thing happen. The bike feels like it's running out of petrol then stops. Try to switch between normal and reserve to re-start it, nothing works. I try again 15 minutes later with the fuel switch set to reserve, and it works fine! I rode home without any problem, having put the fuel switch back to normal.
Any ideas what might be causing this? Could it be a dirty fuel tank? I noticed a bit of rust inside the fuel tank. Do I need to clean the "filter" that is at the bottom of the petrol tank? The bike is from 1986, and I understand it had been staying garaged for quite a while in the past.
Any hints appreciated.