General Discussion

1973 36’ Tournament Fish Twin GM 454s closed cooling. The starboard engine falters right around 3000 RPM under load. Runs fine below that, but once I push past ~3000 it stumbles and won’t climb higher.

What’s been done so far:

• Compression test → all cylinders even.

• Cooling system pressure test → held pressure, no leaks.

• Replaced spark plug wires, fuel filters, thermostat (was missing), and both exhaust manifolds.

• Temps now steady at ~175°F on both engines (with thermostat installed).

• Swapped starboard fuel feed to port tank mid-test → problem stayed with starboard.

• Port engine runs strong with no issues.

• Electronic distributor (no external coil).

Other notes:

• Starboard still puts out more white/light gray exhaust than port.

• Oil pressure normal (60–80 psi).

• Manifolds and risers are are consistent temperatures

distributor? Carb? Fuel?

👉 Has anyone chased down this exact symptom