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  #1   IP: 204.136.203.146
Old 04-29-2019, 12:22 PM
jlobdell12@gmail.com jlobdell12@gmail.com is offline
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1984 Mercrusier 140 Help

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....
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Old 04-29-2019, 04:17 PM
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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.
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Old 04-29-2019, 04:33 PM
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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.
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Old 04-29-2019, 10:41 PM
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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.
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Old 04-30-2019, 06:12 AM
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By Atomic Four standards maybe this also sounds like a blocked exhaust?
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Old 04-30-2019, 10:22 AM
JOHN COOKSON JOHN COOKSON is offline
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$0.02 Worth

Quote:
Originally Posted by ndutton View Post
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
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Old 04-30-2019, 10:33 AM
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It is a car-derived inline 4.
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Old 05-01-2019, 09:46 AM
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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?
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Old 05-01-2019, 11:34 AM
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Carb could be gummed up and leaning out.
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Old 05-01-2019, 11:38 AM
JOHN COOKSON JOHN COOKSON is offline
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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
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Old 05-01-2019, 02:00 PM
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A timing light will confirm that.
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Old 05-03-2019, 07:41 AM
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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?
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Old 05-03-2019, 08:44 AM
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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.
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Old 05-03-2019, 09:53 AM
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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.
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Old 05-03-2019, 11:02 AM
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Quote:
Originally Posted by JOHN COOKSON View Post
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
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Old 05-03-2019, 11:48 AM
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j, pull the distributor cap and give the rotor a twist. It should move abot 15 degrees smoothly and spring back nicely. If not it needs a lube and possibly a cleaning.

Next double check for spark plug wire firing order just to be sure.

The timing should be checked at idle speed in or out of gear doesn't matter as it just needs to be set at idle speed. And by revving the engine you can confirm the centrifugal advance is functioning.

RE the carb, with a fuel bowl full look down the throat of the carb and give the throttle (engine not running) a twist. When you do you should see a small squirt of gas. This will confirm the acceleration pump.

One other possibility is carbon tracks in the dist cap. These tracks can be seen with careful inspection and tracks could cause this very problem. The tracks will offer a path of less resistance (due to compression) to the wrong cylinder.

Get back after these checks.

Dave Neptune
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  #17   IP: 107.77.97.101
Old 05-06-2019, 02:43 AM
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Yea, I figured Dave would know this engie. I think they called it the "Iron Duke". Came in little Chevys. Merc mod was much bigger valves. I rebuilt one just around 1984! Nice engine really.

Sound was cool.
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Old 05-06-2019, 09:37 AM
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Quote:
Originally Posted by lat 64 View Post
Yea, I figured Dave would know this engie. I think they called it the "Iron Duke". Came in little Chevys. Merc mod was much bigger valves. I rebuilt one just around 1984! Nice engine really.

Sound was cool.
Hate to be a downer but not in my experience. The first one cracked the head just before the warranty expired. The dealer said we overstressed it, he sure hoped we didn't try pulling any waterskiers . We bought the boat specifically fore that purpose The second one made it past warranty before it died from continued water ingestion from a bad gasket. By the 600 hour mark we were on the THIRD one Don't know how long #3 would have made it, the boat sank soon after.
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Old 05-06-2019, 01:47 PM
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Not a downer at all. Its a forum for this kind of thing. My experience was only one engine. Good to hear your story. Er, I mean sorry to hear it.
Its just like a dealer to say something like "overstressed".Thats a nothing term for diagnosis. If it can't pull a skier, it just won't pull a skier!
Seems to me there was chronic lack of cooling in the setup. Chevy engines like to crack heads and warp from overheating. But then, so do all engines. At the other end of the spectrum, I have friend that put a merc 140 into a landrover! He pulled a trailer from N. Carolina to Alaska With it.it takes all kinds.

R.
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Old 05-07-2019, 11:29 AM
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Thumbs up The Iron Duke

Lat, ah the venerable Iron Duke. The 4 banger was a great fishing/recreation applications. They would go for many hours with minimal maintenance.

Joe, I had a few friends with 16 foot skiboats using the 4 banger and it just worked them to a quick death. Pulling a skier was a big load for the Duke. The same boats with an IO and the 6 cylinder ran forever.

When working in boat shops we always tried to get the buyers to go for the 6 or a big OB,, they worked better and lasted far longer.

Dave Neptune
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Old 05-07-2019, 05:03 PM
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Quote:
Originally Posted by Dave Neptune View Post
Lat, ah the venerable Iron Duke. The 4 banger was a great fishing/recreation applications. They would go for many hours with minimal maintenance.

Joe, I had a few friends with 16 foot skiboats using the 4 banger and it just worked them to a quick death. Pulling a skier was a big load for the Duke. The same boats with an IO and the 6 cylinder ran forever.

When working in boat shops we always tried to get the buyers to go for the 6 or a big OB,, they worked better and lasted far longer.

Dave Neptune
Our poor runabout got used VASTLY beyond the design brief for a cheap boat to be used in a freshwater lake in calm weather. Besides for waterskiing and tube towing, it ended up doing a few multi-day trips and one memorable long trip at night into seas steep enough that going downhill all you could see through the windshield was green water lit up by the running lights
A friend of mine who happened to work for the company that insured the boat borrowed it one day. The next day I went to use it and found only the bow above water. THAT claim was paid fast with no investigation
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Old 05-17-2019, 03:29 PM
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So if I was to get a V6 what kind of mods would have to be made. Will the out drive fit to the V6?
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Old 05-17-2019, 04:45 PM
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Since there are so many special additions to a auto engine used in a boat, it seems like a good start to get a whole setup surplussed from a repower and go through it and restore it instead of buying all the bits to marinize an auto engine.
You may still have to buy many parts that will be worn or bad on the surplus engine along with a rebuild, but the setup will be a model for what you will want to end up with. A physical parts list if you will.
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Old 05-17-2019, 05:58 PM
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Pretty much all old "Chevy" engines use the same bell housing pattern so that should be no biggie.

The same holds true for many of the motor mounts as far as spacing, again probably no biggie.

Then you will need all of the adaptations Russ mentioned to make it work, not real easy.

Best look for a Mercruiser 6 out there somewhere. There are many as there are many who have also moved up to the V-8's.

Might be easier to sell & buy up too.

Dave Neptune
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Old 05-17-2019, 09:54 PM
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Many years ago I knew a guy who did rebuilds for Mercruiser, primarily 350's. He and I were chatting about it and I asked if all he was doing was marinizing the base automotive engine (that's what it looked like to me) and he said oh no. The alloys of the crank, cam, rods, and gears (maybe more, I can't remember exactly) were completely different to withstand the loads applied with long continuous runs at constant RPM's.
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