1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Jono69

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After a long hiatus guys, I'm back. Having an issue with my 1993 OMC 5.0L HO Ford engine. Holley Carb'ed, mechanical fuel pump. Haven't been able to run it all year but finally getting to it. This thing is running rich. Really rich. Lot's of black smoke and noxious fumes. I can get it to start and run with the throttle at the half to full settings. Runs pretty rough though. And will not run below half throttle setting. I rebuilt the Holley carb at the end of the year last year but never ran it after that. I have turned the mixture screws in, out, everyway. I'm stuck. Any ideas guys?
As always, thank you in advance for any help you can provide.

Jon
 

xjdriver

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Sounds like your float, or floats are stuck in the down position. Try tapping on your carb bowl(s) and see if it helps i dont know if you have a double pumper(two float bowls) or single, but if either one sticks with the needle valve open, it will couse the engine to flood as soon as that mechanical fuel pump gets going.
 

cr2k

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

OR the Power Valve. If the diaphragm is bad they will leak raw fuel in to the engine.
 

Maclin

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

I vote Power Valve. Those are the EXACT symptoms.

Jono, check the oil on the dipstick. It may be higher than it should be and be a bad grey color, and smell like fuel. If so then, after you get the carb fixed and BEFORE running it you need to change the oil. Excess fuel from a leaking power valve goes right into the intake manifold plenum then into any cylinder in reach that has the intake valve open. When the engine is running it can consume the excess fuel but has those driveability and running issues you have. But with the engine off it will leak until the fuel bowl has drained, this can be a considerable amount of raw fuel when you consider the pressurized fuel in the line between the fuel pump and the carb that will come in as the fuel bowl float level drops. In addition to making the next start difficult, that raw fuel will gradually seep past the rings and into the crankcase. Takes the oil on the cylinder walls with it, not so good of a thing to happen for the next startup.
 
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Jono69

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

I see why the powervalve would possibly cause my problem, but don't understand why?! It is new!! Came with the rebuild kit!! I am going to check the timing too, because I think thats off possbily as well. I changed the oil yesterday before I ran it. Haven't looked at the level since. I'm currently at work, but I might run home and grab the boat to tinker with it while on the clock :)
 

Jono69

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

And thank you again guys!!
 

Boomyal

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

All it takes is one back fire up through the carb to blow the power valve. Recent Holleys ( I do not know when it started) come with an anti-blow out modification. This can be retrofitted to older Holleys. It is some kind of check valve setup that keeps the force of the backfire from coming up thru the power valve. I did this retrofit on my Holley. It has never backfired since I did it so I do not know how successful it is.

If the power valve is ruptured, the venturi bores will be soaking wet at an idle.
 

Jono69

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Did some more digging into just about every square inch of this thing. Found I had 2 spark plug wires crossed. Uncrossed them. Timing is where it's supposed to be. Opened up the distributor, everything "looks" good, but cleaned up some contacts. Then it would BARELY run, but runs smoother and only at half throttle and above. Found a significant amount of gas in my oil. Changed oil, for the 3rd time in as many days. No gas in the line to the fuel pump. Purchased a new power valve, installed it, now it will not run at all. Acts like it is really close to starting, but will not grab. I'm about ready to completely lose it.
 

Boomyal

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Were the venturi bores wet at idle? What firing order did you use? Should be 1 - 3 - 7 - 2 - 6 - 5 - 4 - 8 .
 
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Jono69

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

I did not have the ability to be at idle. Only half throttle or above. Maybe got it to run at about 1300 or so. I looked in there once and they looked wet. And yes sir, that is what she she set up with. And I should clarify something from my last post, there is no gas in the "clear" line from the carb to the fuel pump. Not the main fuel line. Plenty of gas there.
 

Boomyal

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Don't know what you mean about the "clear' line from the fuel pump to the carb OR, the 'main' fuel line. Nothing I know has a clear line anywhere. That being said, it sounds like time for a trip down to the autoparts store to get a fuel pressure guage.
 

bruceb58

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Don't know what you mean about the "clear' line from the fuel pump to the carb OR, the 'main' fuel line.
Gas in the clear line would indicate a fuel pump diaphragm rupture which would cause a rich condition
 

Howard Sterndrive

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

has the OP ever experienced this boat running well? or is it new-to-you? Are you doing the firing order around the distributor clockwise or counterclockwise?
 
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Jono69

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Yes sir. I purchased it winter 2011/2012. It ran really well and strong the first half of last years boating season. Lost my job and consequently couldn't afford to run it the rest of the season. Had a couple issues at the end of "my" boating season last year. Was starving for gas. Rebuilt the carb and replaced the fuel filter and stored it until a couple weeks ago. Things are slowly turning around for us and I'm now able to get her going and enjoy it. It seems as though the fuel issue might be resolved, however I may have uncovered another piece in this puzzle in my digging. That being a weak spark. So into the ignition side of things I go. I figured after cleaning all contacts, the next cheapest parts would be a cap and rotor which I hope to purchase tomorrow and install. The coil is new. Counterclockwise on the firing order.
 

Jono69

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Re: 1993 OMC 5.0L HO (Ford) Carbureted Running Excessively Rich

Gas in the clear line would indicate a fuel pump diaphragm rupture which would cause a rich condition

Yes, that's where I was going with that.
 
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