Mercruiser 3.0 Running Problem

[Conor]

I have a Merc 3.0 Alpha One which is running poorly whilst idling and at low rpm,engine starts easily and runs well at high speed,most problems occur at between 200 rpm and 650rpm any ideas?

 

[Boatist]

Re: Mercruiser 3.0 Running Problem

Conor<br />Need many more details to be of any help. Is the engine missing on one cylinder?? Tell us what you mean by running poorly. Low speed miss can be bad Valve, blown head gasket, low speed carb adjustment, timing off. Is it missing, coughing, surging. What year is it and how old is Exhaust manifold and do you run in salt water. If it is missing I would start with a compression check. Also you can pull one spark plug wire at a time and find out which cylinder it is. If number four has low compression and it is missing I have a idea what it could be. Let us know what you find and will see if can help.

 

[Conor]

Re: Mercruiser 3.0 Running Problem

Boat is a 1991 Searay with 3.0 Alpha One Merc<br />Generally used in fresh water.<br />I took it out twice in early May after the winter and it was fine no problems.<br />This weekend I took it out (very stormy here for last month)and the engine started first time so I let it run to warm up I set the trottle to 2000 rpm but the engine kept dying and would only stay running at about 2500rpm.I drove the boat for an hour around the lake it was fine but returning to the slip was tricky as the engine kept cutting out.<br />Back on dry land<br />I examined the spark plug HT cables and found one slightly cracked cable cover to the distributor end of the cable.I restarted the engine with the Leg in a tank of water it ran fine initially then a little rough. I intend to replace the cables on Tuesday and put the boat back in the water on Tuesday evening.I have a feeling that the problem is electrical so I might also change out the spark plugs. I will come back with the results. As far as a blown head gasket goes at the moment the sump oil is clean no sign of any water.<br />Thanks for your help will reply on Tuesday PM

 

[Boatist]

Re: Mercruiser 3.0 Running Problem

Conor<br />With the problem you decribed I do not think it is a valve or blown head gasket. Head gasket can blow many ways one of most common is between cylinders and will get no water in oil just low compression on both cylinders. Valve or head gasket show up more around 600 RPMS.<br />With what you decribed my guess now is more likely a sticking choke or low speed jets in the carb. Good idea to change the plugs as cheap and easy. The wire will usually be more likely to fail at high RPM than low. If start it up at night can usually see and here spark jump. When you change the plugs may give you a good idea of problem. If it is a sticking choke causing it to run real rich plugs should be pretty black. You may want to pull Backflame aresstor and look at choke after warmed up. Love to here what you find.

 

[Conor]

Re: Mercruiser 3.0 Running Problem

Changed all HT cables last night and plugs are due in Thursday <br />I ran engine in tank, it is now running very well,so the new plugs should reaqlly sort it out <br /><br />Lake trial on Thursday PM <br />I will let you know how it goes <br /><br />Thanks <br /><br />Conor

 

[Conor]

Re: Mercruiser 3.0 Running Problem

Changed plugs and cables, boat still running poorly when at low rpm running intermittantly well. Spent 2 hrs skining and engine ran fine did not cut out idled fine. Came to slipway boat backfired and cut 5 or 6 times <br />Any ideas ?

 

[beachcraft]

Re: Mercruiser 3.0 Running Problem

Hi,<br /><br />I wonder why your idling RPM is at 600 RPM. <br />Shoudl it be at 700-800RPM?<br /><br />I have the same engine at the same year and idling RPM is very low, I will adjust my idle needle to make it at least 800 RPM in gear.<br /><br />Regards,<br />BC

 

[russthemuss]

Re: Mercruiser 3.0 Running Problem

hey coner, try giving the carbs a good clean out

 

[Conor]

Re: Mercruiser 3.0 Running Problem

Carb appears to be the problem after speaking to other users they all have had a similar problem a problem with fuel forming a gel in the carb<br /><br />Boat now in dealers and repair bill going to fuel company<br /><br />Best Regards<br /><br />And thanks to all for help