Any tricks for finding a leak in fuel line ?

There are not too many points you could be getting air into the system

1. Fuel pickup tube in the tank might have holes above the sock filter.
2. The hose between sender and body tube
3. Body tube
4. Hose between body tube and fuel pump
5. Fuel pump
6. Hard line from fuel pump to filter
7. Hose between hard line and filter
8. Filter
9. Hose between filter and carb hard line
10. Hard line to carb
11. Any of the misc fittings along the way.

To get air in the system it would need to be before the fuel pump. 1 thru 4 or the fuel pump.

But 2 thru 4 might syphon fuel out of the tank and you would have a fuel leak that would be noticable

The fuel pump might have a leak before it is pressurized but I would expect a syphon leak there too.

Once the fuel is pressurized you would have a fuel leak that would be noticable.

So if you have no visable sighs of a fuel leak my bet is the pickup tube in the tank has a rust hole or a crack.

Or as others have said your fuel is vaporizing in the lines.

I had a similar issue, not that extream, but I could watch my clear fuel filter go empty, engine rpm drop then it would refill.

And if the engine was really hot it would get fuel starved on light to medium acceleration.

All this has been solved by using non alcohol fuel.