F 104 no air getting into fuse too cool battery
 

Any idea on how to fix

A few more details would help.
What F104 is it?
What battery? (mAh, no of cells,, C rating)
Have you measured the current?

Motion RC 90 mm 104 5000 milliamp 6 Cell pack no openings in fuse near battery pulse battery 65 C

Easy fix, cut out good size holes on each side of fuse and cover it up with air scoops using anything you can find practicable like part of some plastic bottle or else. Make sure the air in can also escape out.

FWIW, battery cooling with a large, 6 cell lipo is a bit over rated. If you're flying for 5 minutes, a bit of cooling airflow won't have much effect over the center cell temperatures. Maybe right at the surface where people place temp sensors, but not in the center. Might make a difference if the model flew for 1/2 hour, where cooling airflow could reduce the steady state temperature. Realistically you want batteries for the app that are sufficiently sized/rated, to stay within safe temperatures.