Rough idle when cold-any suggestions?

[UNSUREBOATGUY]

1987 3.0 Mercruiser-the motor starts ok, but idles rough and runs rough at low RPMs. The idle smooths out a lot once the motor is warm. Any suggestions for what to look at first? Seems to run just fine at higher RPMs. The plugs say it is running rich. Thank you.

 

[steddy]

Re: Rough idle when cold-any suggestions?

Mine did, too. Choke adjustment, maybe. Mine smoothed out after a few boating trips. It was laid up for 3 years when I bought it. It didn't idle but rough when warm, and not at all when cold. A few tanks of fresh fuel through it did the trick.

 

[Bondo]

Re: Rough idle when cold-any suggestions?

Ayuh,... Sounds like the Choke needs attention...

 

[Don S]

Re: Rough idle when cold-any suggestions?

Give it a little throttle while it's warming up. Carbed engines tend to load up a 500 to 700 idle rpm when cold with the choke on.
Raise the rpm (Throttle lever) up to 1000 to 1200 rpm for warm up and it will run a lot better.
The 3.0L engines are not EFI like your car or truck where you just hit the key and go.

 

[180shabah]

Re: Rough idle when cold-any suggestions?

Rough idle when cold-any suggestions?

...warm it up????

 

[UNSUREBOATGUY]

Re: Rough idle when cold-any suggestions?

Thanks for the input guys.

 

[myoldboat2]

Re: Rough idle when cold-any suggestions?

I just warm mine up to 130 degF on the gauge by idling at 1200 to 1500 rpm. Only takes a few minutes. People who complain about it at the ramp are told to mind their own business. If they get snotty about it then I really take my time.