75 T-Spark engine cutting out @ medium revs

[DBonelli]

What could be happening with a Twin Spark that seems to feel as if it has a rev limiter on it at 4000 RPM? The car drives fine until you hit 4 when it jutters and wont go any higher. A timing issue, or something else? This is not my car, one I was looking at.

[Tastarga]

Sounds like a fuel problem - dicky fuel pump, blocked fuel filter or similar.