engine idles real rough when cold, smooths out with when throttled up

N

natsgrampy

Petty Officer 2nd Class
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Aug 31, 2010
Messages
172
Have an 87 sea ray with a mercruiser 3.0 sterndrive.

When it is started cold, it rattles, shakes, and even stalls unless the throttle is increased.:mad: Once it is warmed up, it idles fine.

I pulled a sparkplug, which was installed new at the beginning of the season, and it was black.

I tried to find a thread about a black plug and couldn't. Could this be the points, condenser, distributor cap, wires, all of the above. Or, am I looking in the

wrong area?

Could it be an incorrect adjusted carbeurator?

Also, I have installed a water seperator filter, which this never had before. Should I remove the filter out of the fuel pump, or leave it in there?
 
Don S

Don S

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62,321
Re: engine idles real rough when cold, smooths out with when throttled up

Sounds normal to me, cold engine, choke on, low idle speed, all together equals rough idle.
Just speed the engine up to 1000 to 1200 rpm and let it warm up, then go to idle.
 
reavesga

reavesga

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Feb 14, 2010
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Re: engine idles real rough when cold, smooths out with when throttled up

Agree with Don. Same on my 140 HP Mercruiser. Normally I leave the boat hooked to the trailer and fire the boat up. I sit there and let her warm up for about 5 minutes at 1000-1200 rpm. Then bring the warm up lever back and make sure she idels. Finally I put it in reverse and make sure she keeps running. ALL of this before I unhook off the trailer. Of course I take it out of gear before I go forward to unhook from the trailer.
 
J

John_S

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Re: engine idles real rough when cold, smooths out with when throttled up

If you are pulling it back to idle as soon as it fires, its going to run rough. For good measure, check your choke operation and closed gap, and for opening fully when warm. Also, check your plugs again after the end of the next outing. If they are still black then you may have a rich running condition. Usually a carb issue or mech fuel pump leaking and venting gas into carb.
 
F

Fordiesel69

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Re: engine idles real rough when cold, smooths out with when throttled up

Pretty normal this time of year.........

My inline 6 has a similar carb and choke stove, although it only takes 2 min during the summer to warmup, I now find it more like a full 5 min now that it is in the low 50's around here and so is the water.
 
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natsgrampy

Petty Officer 2nd Class
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Aug 31, 2010
Messages
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Re: engine idles real rough when cold, smooths out with when throttled up

Thanks for the info! I thought I had a major issue, guess I don't. I will still replace all the aforementioned ignition parts.

Great forum all, keep up the great work.
 
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