johnson j50dtleca starts then idles roughly

[AV Doogie]

I have a 50hp -3 cylinder engine which recently developed an idling problem. The engine starts nicely and idles for about one minute ...then begins to run extremely rough as though an air leak or fuel starvation sets in. The engine can run this way for a few minutes before it stops. I notice the fuel filter has air in it after shutdown. Upon priming the fuel bulb, the fuel filter refills and the engine will start and idle nicely for another minute. Is this a fuel pump issue?


Thanks for any help.

[AV Doogie]

Update: upon further investigation I have found the following.

I tried spraying carb cleaner into the carbs with engine running. The top and bottom units tend to cause the engine to stop. Spraying carb cleaner into the center unit causes the engine to run smoothly for a short period of time. I can maintain smooth running if I spray this carb upon start of rough running. This now sounds like a carb problem..... Any ideas where to look on the carb?

[AV Doogie]

Took out the center carb and inspected/cleaned the unit. I found nothing out of the ordinary with this carb. The low speed screw was adjusted to 1.75 turns out. The needle valve looked like new and the carb was very clean.

Reinstalled the carb and attempted to run the engine. The engine performs similarly to above except now adding carb cleaner to any of the the three carbs while running causes a short term smooth run.

Now I am back to the fuel pump as an issue. Any Ideas here folks?