Losing RPM's for short periods of time...

[mmcguire2002]

Recently, my Port engine will take longer to get up to cruising RPM's than starboard and once on plane, it will occasionally drop rpm's for 5 to 10 seconds and then come back up. Any idea what could cause this? :huh: Fluids and filters all changed since this started occurring. Any ideas appreciated.

 

[KC_Sundancer]

I've had a fouling spark plug do this.
Could be a plug wire issue too.

 

[Captain Allen]

I had something similar to happen. Turned out to be the fuel pump going bad. A new one solved the problem. Keep in mind that my fuel pumps are mechanical and my engines are carbed, not EFI.

 

[mmcguire2002]

I'll check on the plugs. Thank you for the suggestion.

 

[tbontrager]

I had similar problem on a Mercruiser 350 mag. Previously ran fine for 3 hrs then got worse over time. Ultimately, after ~30 minutes at cruise the RPM would drop off below 1K and then would run fine at <2000 RPM. Engine was not throwing any codes. Turned out it was the low pressure fuel pump.

 

[carterchapman]

Micheal, my 8.1s on my previous 340 were "plug eaters" - until I stopped using AC Delco's. How long since you've changed them?

 

[mmcguire2002]

It's been quite a while. I'll look into changing them and see if that solves the problem.

 

[Kreole Kid]

The Champion plug I switched over to is a "13" RS14YC6. Those plugs are still in the boat and have ran with no issues for a couple of years now.