3GM30F Intermittant Stumble

What’s Happening , I was running my engine for a warm up and battery charge, and after 15 minutes of 1200 rpm, in fwd gear, my engine “stumbled” like it started missing on one cylinder.

This happened briefly , but since it never happened before I was alarmed.

I checked the obvious , fuel level in the Racor sight bowl, and no plastic bag on the prop.

It didn’t drop RPM like when I run out of fuel , but the engine recovered and performed as usual for a while , then it happened again , later again , but each new happening the event was shorter .

Any ideas out there to help me understand this unusual event ?

The most likely causes:

  1. Air bubbles or contaminant in the fuel line
  2. Lack of air to the pistons

If you have recently run out of fuel, it is probably bubbles or contaminant in the fuel line.

Check fual and air hoses for any kinks; they can collapse.

Less likely causes are:
Faulty injector - this will usually generate smoke at the exhaust
Bearing failing on water pump or alternator
Cutlass bearing problem