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5.0 OMC 4-barrel cuts out under load

mike garrett

New member
Motors bogs down or cuts down under load and is now starting to cut out even when idling.When its not cutting out it runs perfect under load, its intermittent
 
If this were my boat i would run it on a external tank of fresh fuel. If the problem disappeared then i would go after the fuel system.

If it is the fuel system meaning water and gunk in the tank i would clean the entire system.

I pumped all the fuel out of my onboard fuel tank when i got it.

You can do one of 2 things, pump the water out of the bottom, or all the fuel out and here is how.

If you just wish to pump just the water out of the bottom of the fuel, you will need to purchase a cheap electric fuel pump from any auto store dc powered.
You will also need about 15 foot of cheap fuel hose from the auto store and clamps to fit the fuel pump.

Install the hose on the fuel pump both ends and cut about five feet on the sucking side of the pump just look for the arrow on the pump.

Remove the fuel pickup tube it's the one where the fuel hose hooks to the tank a 90 degree angel fitting, it's a anti-siphon valve. Unscrew it.

Crank the bow of the boat all the way up, and stick the hose connected to the electric fuel pump 5 feet into the bottom and back of the tank.

Into a clear container pump the water out till you see clean fresh fuel and stop the pump.

Or into a large container pump all the fuel out.

Now check the valve by blowing thru it, check the screen thats its clear.

Install the valve and pickup tube your done.

Question do you have a fuel water separator on the boat, good to have.

If yes replace the element.

If you have a bell type fuel pump clean the filter in that.

There is a filter in the fitting that enters the carb.

And finally i would rebuild the carb. Click on the link.

http://www.marineengine.com/boat-forum/showthread.php?390778-Fuel-Problems-Help&p=338631#post338631
 
If this were my boat i would run it on a external tank of fresh fuel. If the problem disappeared then i would go after the fuel system.

If it is the fuel system meaning water and gunk in the tank i would clean the entire system.

I pumped all the fuel out of my onboard fuel tank when i got it.

You can do one of 2 things, pump the water out of the bottom, or all the fuel out and here is how.

If you just wish to pump just the water out of the bottom of the fuel, you will need to purchase a cheap electric fuel pump from any auto store dc powered.
You will also need about 15 foot of cheap fuel hose from the auto store and clamps to fit the fuel pump.

Install the hose on the fuel pump both ends and cut about five feet on the sucking side of the pump just look for the arrow on the pump.

Remove the fuel pickup tube it's the one where the fuel hose hooks to the tank a 90 degree angel fitting, it's a anti-siphon valve. Unscrew it.

Crank the bow of the boat all the way up, and stick the hose connected to the electric fuel pump 5 feet into the bottom and back of the tank.

Into a clear container pump the water out till you see clean fresh fuel and stop the pump.

Or into a large container pump all the fuel out.

Now check the valve by blowing thru it, check the screen thats its clear.

Install the valve and pickup tube your done.

Question do you have a fuel water separator on the boat, good to have.

If yes replace the element.

If you have a bell type fuel pump clean the filter in that.

There is a filter in the fitting that enters the carb.

And finally i would rebuild the carb. Click on the link.

http://www.marineengine.com/boat-forum/showthread.php?390778-Fuel-Problems-Help&p=338631#post338631

well i did all that and it still has same problem also noticed the coil gets a bit warm car mec told me it could be the ign module what do you think
 
intermittent usually says electrical, which could mean bad connection somewhere. If the module is looking melted or plastic swollen, that would help seal the diagnosis, but that would tend to get worse with run time and temp - not usually intermittent.
You could try a run with the esa disconnected and try with the tachometer disconnected.
 
I had this problem with my 1993 4.3 a few years back. Idled fine but bogged out under load.
Went through just about everything, adjusted pick up coil gap, replaced coil, plug wires, rebuilt carburetor, didn't bother with the spark plugs because they weren't that old maybe like 6 month's.
Well low and behold it was the plugs!
Didn't figure that out until I pulled them out and inspected them. Saw what looked like a crack running up the porcelain on a few of them.
I cleaned the porcelain and rubbed a black magic marker all over the white porcelain. Then wiped it off and did verify that the plugs were cracked because the magic marker soaked into the cracks.
without the magic marker they were almost invisible to the nekkid eye.
New set of plugs and she ran like a new boat again.
Hope this helps.
 
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Do NOT use a 12 volt electric pump to remove your fuel. :mad:

Instead, remove the anti-siphon valve and replace it temporarily with a straight barbed fitting.
Connect a long enough hose to the barbed fitting, and start yourself a siphon, and empty the fuel tank into carry cans outside of the hull.

Keep in mind that if water does exist in your fuel, and unless it has become mixed..... it will be the first liquid to come out of the tank.

At the bottom of the dip tube, you may see a screen. Make sure that this screen is clean and is not restricting fuel flow.
Put this all back together with a new fuel filter, and you will not need to use an external outboard fuel tank.


.
 
Under load with someone else at the helm disconnect the esa module from both micros.

To come out of gear you will have to shut off the engine with the micro's disconnected.

Post back we will go from there.

Don't buy anything yet !!!
 
Need some help I have a 1992 Four Winns Horizon 200 with a 5.0L OMC Cobra V8. I put a brand new 4 barrel carb and a cam. Boat ran fine when I first took it out on the lake it would get up and go, but after the second time of taking it out it back fired 3 or 4 times in a row and now it doesn’t want to get up on plain sometimes. I’ve tried everything. I’ve put a new distributor, plug wires, and I’ve tried 4 different carbs. I started with a 600cfm Holley with worked great up until it back fired. Then I went to a 650cfm Edelbrock, and now I’m at a 750cfm Edelbrock. So far it likes the 750 but it still doesn’t run like it did before. Used to be able to hit 45mph around 4500rpm now I can’t get over 30mph at about 3500rpm.
 
Welcome. A couple things first. You really should have started a new thread specific to your issue. And second, I'm not a mechanic, I'm just another boat owner who prefers to do his own maintenance whenever possible.

You replaced your distributor. What distributor did you install? I'm asking that because I swapped my distributor with a Voyager EST type replacement, and not long after I started having backfire through the carb on acceleration and sluggishness at higher RPM. I found that the module inside the distributor was no longer providing the progressive timing advance that it should have. I then bought a cheap replacement module, and after a short period of time, it too was not advancing. After a lot of Googling, I found that people are having success with the AC Delco module, which would have been used in a genuine OEM Delco Voyager distributor. I've had no trouble since I replaced the module.

So, regardless of the distributor manufacturer, my advice is to check your progressive timing advance. I was getting only about 16 degrees of advance (as I recall) from 1800 RPM and up.

If you do have the Voyager EST type distributor, the AC Delco module part number I'm using is D1965A.
Delco Voyager module D1965A.jpg
 
a 5.0l engine spinning a sterndrive can't use a 750 CFM carb...the 600 CFM is a better option but still on the large side.

what cam did you put in? If you went much larger in duration from the stock cam you likely shifted the power band of the engine too far up the RPM curve...
 
Welcome. A couple things first. You really should have started a new thread specific to your issue. And second, I'm not a mechanic, I'm just another boat owner who prefers to do his own maintenance whenever possible.

You replaced your distributor. What distributor did you install? I'm asking that because I swapped my distributor with a Voyager EST type replacement, and not long after I started having backfire through the carb on acceleration and sluggishness at higher RPM. I found that the module inside the distributor was no longer providing the progressive timing advance that it should have. I then bought a cheap replacement module, and after a short period of time, it too was not advancing. After a lot of Googling, I found that people are having success with the AC Delco module, which would have been used in a genuine OEM Delco Voyager distributor. I've had no trouble since I replaced the module.

So, regardless of the distributor manufacturer, my advice is to check your progressive timing advance. I was getting only about 16 degrees of advance (as I recall) from 1800 RPM and up.

If you do have the Voyager EST type distributor, the AC Delco module part number I'm using is D1965A.
View attachment 24252

Sorry I’m new to this whole form thing and wasn’t sure how to create a new thread.
I will upload a picture of what distributor I have on the boat. I have a couple videos of what the boat sounded like at idle when I first got the boat running with the new cam, and carb and one about 2 weeks later after it started running like crap.

The cam duration is 269/277 and lift is .475/.496
Carb I had on it at the time was a Holley 600CFM

The boat ran great on the water for the first couple times I took it out but on the third time if when it back fired a few times and had a hard time getting on plain with more than 3 people.
 
Well I cant get the Videos to upload now, but the first video was showing how smooth the engine ran and the second one showed how rough the idle was after the back firing. It basically sounded like it had a much bigger cam than it did.
 
that cam isn't too bad. I'd check the ignition to make sure the timing is advancing with RPM and to make sure the spark is consistent...its likely to be either fuel or ignition and you just have to troubleshoot it vs throwing parts at it...

A boat engine has a lot higher (and consistent) load on it than a car...if anything is marginal it will tell you real fast...
 
vacuum advance means AUTO, not MARINE, application for a distributor....I would change that as soon as feasible....
 
I mean I can put the old distributor back on but it will still run like crap. That’s why I changed it out thinking it was the distributor. The only other thing that maybe would cause omit to run bad would be that little computer thing that mounts to the exhaust riser. Not really sure what that does.
 
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