Dies when you get up to highway speeds
I recently bought a 76 f250 super cab with a 460. The truck ran ok in town I recently bought a 1976 F250 super cab with a 460. It ran fine in town but when I got it on the highway it flooded out and died. The air filter was clogged so I figured that was it. I replaced it and it ran fine for a few trips then it happened again today twice when I gave it more gas. Both times when I removed the top of the breather it fired right up. I was thinkin it could be bad gas but why would it start without the breather? Any ideas? I posted this yesterday on new forum but thought this was a better place.
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Did you notice if the choke butterfly in the top of the carburetor throat was staying open? If that butterfly can move around and close it will choke off the engine due to lack of incoming air. Let us know what you found.
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Originally Posted by hanky
(Post 98354)
Did you notice if the choke butterfly in the top of the carburetor throat was staying open? If that butterfly can move around and close it will choke off the engine due to lack of incoming air. Let us know what you found.
The one that switches from exhaust to cold air. |
There is supposed to be a temperature sensor in the air cleaner housing. Some are vacuum controlled and others don't use any vacuum. When the engine is cold the incoming air to the carb is supposed to come up from the exhaust manifold through a snorkel and into the air filter. Once the sensor determines the air is warm enough it opens the snorkel to outside air. If the electric choke is not heating the element to hold the choke open the force of the incoming air will close the butterfly and starve the engine for air. I believe that is probably the only thing causing problems. That wire comes from one of the alt terminals . If you correct the electrical connection it should take care of the choke problem.
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Originally Posted by hanky
(Post 98356)
There is supposed to be a temperature sensor in the air cleaner housing. Some are vacuum controlled and others don't use any vacuum. When the engine is cold the incoming air to the carb is supposed to come up from the exhaust manifold through a snorkel and into the air filter. Once the sensor determines the air is warm enough it opens the snorkel to outside air. If the electric choke is not heating the element to hold the choke open the force of the incoming air will close the butterfly and starve the engine for air. I believe that is probably the only thing causing problems. That wire comes from one of the alt terminals . If you correct the electrical connection it should take care of the choke problem.
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As far as I know that door, as it is called, does not rely on air to make it open. If the mechanism to make it open is missing, just find something to hold it open. It is only needed when starting the engine in cold weather.
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Originally Posted by hanky
(Post 98358)
As far as I know that door, as it is called, does not rely on air to make it open. If the mechanism to make it open is missing, just find something to hold it open. It is only needed when starting the engine in cold weather.
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Are you sure it is getting overfueled? You are telling us it flooded out , that would mean being overfueled. Could it be starving for fuel ? High speed places more demand for fuel . Insufficient fuel could be caused by a partially plugged fuel filter. Did you check that out? A 460 needs a lot of fuel and maybe it isn't getting enough at higher speeds.
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Please check to see if your fuel cap is vented. I think Hanky is on to something with starving for gas and a non-vented fuel tank would do that.
Eric |
Thanks Eric,
Just goes to show you , you can't think of everything ! Very possibly a simple thing like the wrong fuel cap. |
Originally Posted by hanky
(Post 98374)
Thanks Eric,
Just goes to show you , you can't think of everything ! Very possibly a simple thing like the wrong fuel cap. I talked to myf father in law about the problem and he thought it was a vacuum issue. I sprayed starting fluid around the carb when the truck was running and it revved up. Rebuilt the carb and it runs and idles but it is missing on 2 cylinders since I changed the plugs. I changed the wires but it didn't help. I found 1 of the plugs to be fouled but haven't pulled the other. Can a plug foul if a wire isn't working? |
Yes if the plug is not getting any voltage and thus no sparking it will foul.
A couple of thoughts on plugs. They are not necessarily gapped correctly out of the box The seat where the plug screws in HAS to be perfectly clean as that is where the ground connection occurs. If it is dirty then you get a poor electrical connection and thus poor spark, Plug wires should be checked with a volt meter for resistance or by easing the wire off and holding near the block while the engine is running. You should get a nice crisp blue spark. If your plugs have small screw on tops then they need to be quite tight as well. Champion plus used to use that arrangement. If the top ferrel is loose you get a poor electrical connection. Regards, Eric |
Originally Posted by eric hoffmeyer
(Post 98662)
Yes if the plug is not getting any voltage and thus no sparking it will foul.
A couple of thoughts on plugs. They are not necessarily gapped correctly out of the box The seat where the plug screws in HAS to be perfectly clean as that is where the ground connection occurs. If it is dirty then you get a poor electrical connection and thus poor spark, Plug wires should be checked with a volt meter for resistance or by easing the wire off and holding near the block while the engine is running. You should get a nice crisp blue spark. If your plugs have small screw on tops then they need to be quite tight as well. Champion plus used to use that arrangement. If the top ferrel is loose you get a poor electrical connection. Regards, Eric |
Do an ohms meter (resistance) check on the wires
Look carefully at the towers in the distributor cap for any arcing marks. If the inside of the distro (gosh does this truck HAVE a distributor) any scratches inside the cap are grounds for tossing it. Scratches will be tracks that the voltage will flow on versus getting to the spark plugs. |
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