I have a 01 Heritage Softail. Last week I ran it till the low fuel light came on. After filling up I started to notice that it wasn't running right. Its been backfiring both through the intake and the exhaust. I have also noticed that tge fuel mileage has droped by 20 miles per tank. There is also a sucking noise from the frount.

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Check your vacuum lines.
The Vacuum leak can sometimes be found with starting fluid. RPM's will increase when sprayed at the leak.

I have a 01 Heritage Softail, I thought I had a vacuum leak. I don't. It still sounds like it but I checked all the lines. I have paid closer attention to what its doing. It still back fires and cackles a lot but only when I get below a half tank. I have tried to put 92 octane gas in and injector cleaner, but still no change. I have sprayed eather around the gas lines, no change. I have ruled out electronics do to the problem is only there at a half tank.
What next?

Clogged fuel lines/filter?