Dies under a load!
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Joined: Nov 2009
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Dies under a load!
I have a 79 F250 with a 400. I finally have it running after finding some major mistakes made by the previous owner. My issue is that although I am still idling a little rough, as soon as I take it out of park and put a load on it in idle it dies. If I keep the gas to it I can keep it running and drive it around the block, but everytime I go to the brakes or fully let off the gas it dies. I would appreciate any thoughts. The truck is in rough shape right now, but once I get it running well it is body work time. Thanks for the help.
Elder User
Joined: Aug 2004
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You have to start with the basics. Air, Fuel, and Spark. Air is pretty much the easy one.
I would really consider spark the next easiest. Make sure your plugs, wires, cap, rotor, and points (if it has them) are in good shape. Make sure the timing is set properly for your truck.
If none of that helps, you may have a fuel related problem. If you haven't done so, buy the kit and go through the carb. In addition to having the gaskets needed to put the carb back together, they tend to have instructions on how to set it up properly for your engine. For example, my 2bbl was used on many different engines. Some moron had set up the accelerator pump for something like a 400 big block, while it's just a little 302!
When you have the carb off check for any rust and stuff in the bowl, as this could be an indicator of rust in your tank / lines. I would also turn the fuel line up into a clear jug and crank the engine a little bit to make sure the fuel pump is pumping an adequate flow. Also while the carb is off, look at any of the vacuum lines for leaks, and check the EGR to make sure it's not stuck open.
Put it all back together and go through the procedure for properly setting the choke and the idle air mixture. When you get done your engine may run like a champ, it may not. If not, then you'll probably need to start looking other places, such as vacuum leaks around the intake manifold, compression, etc.
I would really consider spark the next easiest. Make sure your plugs, wires, cap, rotor, and points (if it has them) are in good shape. Make sure the timing is set properly for your truck.
If none of that helps, you may have a fuel related problem. If you haven't done so, buy the kit and go through the carb. In addition to having the gaskets needed to put the carb back together, they tend to have instructions on how to set it up properly for your engine. For example, my 2bbl was used on many different engines. Some moron had set up the accelerator pump for something like a 400 big block, while it's just a little 302!
When you have the carb off check for any rust and stuff in the bowl, as this could be an indicator of rust in your tank / lines. I would also turn the fuel line up into a clear jug and crank the engine a little bit to make sure the fuel pump is pumping an adequate flow. Also while the carb is off, look at any of the vacuum lines for leaks, and check the EGR to make sure it's not stuck open.
Put it all back together and go through the procedure for properly setting the choke and the idle air mixture. When you get done your engine may run like a champ, it may not. If not, then you'll probably need to start looking other places, such as vacuum leaks around the intake manifold, compression, etc.
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