Sudden Engine Problem - 351w
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Junior User
Joined: Jun 2007
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Sudden Engine Problem - 351w
1983 351w 4 Bbl
All a sudden, it wont stay running, I started it up and it would not rev, it was running super rich, gagging itself, no choke changing or flooring it, would get the rpm's above 2000 rpm, flooded easy, it would not stay running.
I pulled the fuel filter from the in-line by the carb, clean as a whistle.
Not the choke, not the fuel pump, what? Valves?
Any advise welcome.
All a sudden, it wont stay running, I started it up and it would not rev, it was running super rich, gagging itself, no choke changing or flooring it, would get the rpm's above 2000 rpm, flooded easy, it would not stay running.
I pulled the fuel filter from the in-line by the carb, clean as a whistle.
Not the choke, not the fuel pump, what? Valves?
Any advise welcome.
Mountain Pass
Joined: Jul 2010
Posts: 105
Likes: 1
From: Honolulu, HI
Set screws set too far open? When was the carb rebuilt? My experience is with the Motorcraft 2150A 2B feedback carb with EEC-IV. I'm not too familiar with the 4 bbl setup. If its running rich carb would be the first place to look. Does it run better when at operating temp? Have you checked the engine with a vacuum gauge? This will tell us if the engine is mechanically sound.
Too many variables at the moment to pinpoint a specific issue. At least for me.
Too many variables at the moment to pinpoint a specific issue. At least for me.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
I dunno since it happened all at once, out of the blue still inclined to think the needle and seat may have a piece of crud or hose or something or jammed up somehow. Since it's a fuel problem it almost has to be internal to the carb? That's my WAG, and stickin' to it.
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Elder User
Joined: Feb 2014
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From: Lincoln, NE
The air intake system is the air filter and everything else related to the air entering your carburetor.
With the air cleaner removed, try starting the engine or have it running and then look down the throat of the carburetor. Shut the engine off while still observing the throat. After the air stops flowing you should not see and fuel 'dripping' from anywhere in the throat. If you do, the fuel level is too high and is flooding the engine with too much fuel.
You can pinch off the rubber line between the fuel tank line and the fuel pump to restrict the fuel to the pump and carb. This would then confirm that the needle and seat in the carb is not able to control the fuel level.
With the air cleaner removed, try starting the engine or have it running and then look down the throat of the carburetor. Shut the engine off while still observing the throat. After the air stops flowing you should not see and fuel 'dripping' from anywhere in the throat. If you do, the fuel level is too high and is flooding the engine with too much fuel.
You can pinch off the rubber line between the fuel tank line and the fuel pump to restrict the fuel to the pump and carb. This would then confirm that the needle and seat in the carb is not able to control the fuel level.
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From: Boise, Idaho
I'm with Tedster on this. It's an internal issue on the carb.
What style of carb do you have? Is it a Holley? Edelbrock?
If it's a Holley, remove the site plugs from the fuel bowls while it's idling and see if gas comes pouring out. If so, then your float isn't stopping the gas from coming in. If that's the case, you either have a bad float, or junk in the needle and seat.
Also, when you say it's new, do you mean "rebuilt new" or "brand new"? If rebuilt, (and again a Holley), you may have a blown power valve. New Holleys (after around '93) all have protection against that.
What style of carb do you have? Is it a Holley? Edelbrock?
If it's a Holley, remove the site plugs from the fuel bowls while it's idling and see if gas comes pouring out. If so, then your float isn't stopping the gas from coming in. If that's the case, you either have a bad float, or junk in the needle and seat.
Also, when you say it's new, do you mean "rebuilt new" or "brand new"? If rebuilt, (and again a Holley), you may have a blown power valve. New Holleys (after around '93) all have protection against that.
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Thanks for all input. Happy Fathers Day (if applies)
This morning I removed both needle valves, soaked them in alcohol cleaned them and put them back in. Did not help. Will start, will idle (barely) but the proble persist. Can not get the RPM's up at all, will not rev, weird. Carb is a Factory rebuilt Holly.
This morning I removed both needle valves, soaked them in alcohol cleaned them and put them back in. Did not help. Will start, will idle (barely) but the proble persist. Can not get the RPM's up at all, will not rev, weird. Carb is a Factory rebuilt Holly.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
"Neede valve", the issue referred to there is the float, needle valve, and seat that regulates the main flow of fuel into the carb bowl from the pump, not the idle mixture screws. More on that later though.
The float needle seat can get a piece of grit or whatever in there lodged, and hold the valve partially open causing it to flood. One trick to try and dislodge this without disassembly while at idle, pinch a section of rubber fuel hose completely closed for several seconds choking off the fuel going to carb, and release. The idea here is to send a nice sudden slug of fuel into the carb all at once and hopefully dislodge the obstruction.
Removing/cleaning the idle mixture screws won't hurt anything, but to do it right you want to send a jolt of carb cleaner through there as well.
The float needle seat can get a piece of grit or whatever in there lodged, and hold the valve partially open causing it to flood. One trick to try and dislodge this without disassembly while at idle, pinch a section of rubber fuel hose completely closed for several seconds choking off the fuel going to carb, and release. The idea here is to send a nice sudden slug of fuel into the carb all at once and hopefully dislodge the obstruction.
Removing/cleaning the idle mixture screws won't hurt anything, but to do it right you want to send a jolt of carb cleaner through there as well.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
OK. So you disassembled. Floats aren't fuel logged, set float height, passages are clean and the rest of it?
Didja replace the power valve as mentioned above, as long as you were in there good idea, no? Maybe the stuff they call fuel these days ate through it, I dunno. Gotta be something basic and simple.
Didja replace the power valve as mentioned above, as long as you were in there good idea, no? Maybe the stuff they call fuel these days ate through it, I dunno. Gotta be something basic and simple.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
OK. Then I'd pull the carb and start from scratch. Take pictures of linkage and how everything is connected to help get it back together just like it should be. Put a rag in the intake to keep anything from falling in there.
Then, take the LIST # that is printed on the air horn, and download the free manual .PDF from Mike's Carburetors or wherever on that carb, and study it. Watch some YT videos and such. Checkout some other websites on carb repair and tuning. You'll be up to speed in no time and get it dialed in better than ever.
If the needle and seat is real old, it may simply be worn out too. Carbs are pretty simple overall, a few quirks but they respond really well to a little TLC.
Then, take the LIST # that is printed on the air horn, and download the free manual .PDF from Mike's Carburetors or wherever on that carb, and study it. Watch some YT videos and such. Checkout some other websites on carb repair and tuning. You'll be up to speed in no time and get it dialed in better than ever.
If the needle and seat is real old, it may simply be worn out too. Carbs are pretty simple overall, a few quirks but they respond really well to a little TLC.