1984 Mercrusier 140 Help

[jlobdell12@gmail.com]

I have a 1984 Mercruiser 140 3.0 that I am having a issue with. So the engine will start and run fine on a hose, sounds good no knocking or any out of the ordinary sounds. I can give give it gas and it will do just fine. Once I put it in gear and give it gas it will spit and sputter but will accelerate. Once I put it in the water I can start it and it fires right up and sounds great. Once I put it in gear and try to accelerate it falls on its face back fires thru the carburetor and dies. It will start right back up and still idle great. It will only die when accelerating under a load. So far we have checked the fuel pump and it is fine, replaced the ignition coil, points, distributor cap, rotor, spark plugs, Checked compression (Good), Set timing, fuel filter, changed gas out (even have it hooked to external tank), new carb, set bowl level to the book. Not sure where else to turn. Any help would be appreciated....

[ndutton]

Based on your symptom set I would double check the timing. It sounds to me like it is way advanced to start with and only gets worse as the RPM increases due to whatever advance mechanism that engine has. The firing back through the carb tells me you are getting ignition with intake valves open.

[joe_db]

I was thinking also the accelerator pump????

BTW - those engines are HUGELY prone to leak water into the oil. Mine got so bad I would put a container under the engine and drain about 3-4 quarts of water before starting it
Check the oil EVERY day and watch for it going up. If you don't do that and there is water in there, starting the engine mixes the water and the oil to bad effect.

[Mo]

I haven't worked on a merc but my own Suzuki had a similar problem when I first got it. Couldn't find the problem for the longest while...turned out to be a fuel filter installed backwards. Turned that around once I saw the arrow in the wrong direction and it was fine.

[tenders]

By Atomic Four standards maybe this also sounds like a blocked exhaust?

[JOHN COOKSON]

$0.02 Worth

Based on your symptom set I would double check the timing. It sounds to me like it is way advanced to start with and only gets worse as the RPM increases due to whatever advance mechanism that engine has. The firing back through the carb tells me you are getting ignition with intake valves open.

I know nothing about this engine. If it were an A4 I would suggest check the spark plug wire firing order.

TRUE GRIT

[joe_db]

It is a car-derived inline 4.

[jlobdell12@gmail.com]

So should timing be checked and adjusted while its under a load or at idle on the hose? He said the timing is set and while boat it at a idle on the hose it sounds great. You can accelerate while in neutral and when you put it in gear it idle fine but soon as you give it gas it spits and sputters and dies if you give a lot of gas. On the hose while in gear if you ease into it slowly it will accelerate but if you go to fast it dies and back fire thru the carb. While in the water it will start and idle fine and accelerate in neutral but when you put it in gear and give in any gas at all it will die and back fire thru carb. If the firing order is off will it run good at a idle?

[joe_db]

Carb could be gummed up and leaning out.

[JOHN COOKSON]

If the engine has a spark advance ( I bet it does but I don't know the details) it is probably not advancing off idle setting because it is somehow not functioning correctly.

TRUE GRIT

[joe_db]

A timing light will confirm that.

[jlobdell12@gmail.com]

So we adjusted the bowl level and it started to get a lot better. While doing this it started to miss on the #1 Cylinder and developed a water leak around the thermostat housing (still trying to make sure where it is coming from). Pulled the plug and it seems to have a strong spark, checked compression and compression dropped from about 139 to 115. To me that don't make a lot of sense to have strong fire but have a miss unless i'm missing something. Motor temp only got to about 120 deg so it was not over heating but once it cools down and you start it back up the miss is gone till it gets warm again. So the plan today is to continue to adjust the bowl level till we can get it running right and then look at where the leak is coming from. We don't see any water in the oil or cylinders so once we figure that out we will try and chase down this issue with it missing when it gets warmed up. Any thought on this?

[zellerj]

How about plug wires? Can they be the culprit? You did not mention wires in your initial post.

You also did not mention condenser. Sometimes they can screw up after getting warm.

[jlobdell12@gmail.com]

I have not changed the wires but they look good and I was told they were replaced when I bought it. I will just change them to eliminate that as a culprit. We are also going to replace the rotor, condenser and points and cap to eliminate that as well. That water leak has me worried a little bit. No water in the oil but it is coming out pretty steady behind the the reservoir on what appears too be the thermostat housing.

[Administrator]

If the engine has a spark advance ( I bet it does but I don't know the details) it is probably not advancing off idle setting because it is somehow not functioning correctly.

TRUE GRIT

+1.

Bill