1979 Ford Brono
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1979 Ford Brono
Questions, just looking for some suggestions. I have a 1979 Ford Bronco, it starts right up, runs good until it gets warmed up then it starts to cut out and sputter and acts like it starving for fuel. I have replaced the fuel filter on carb, thermostat and fuel lines.
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Joined: Jun 2010
Posts: 16,662
This is what I think could be taking place, and I could be wrong !
When the engine is cold the choke is partially closed and addl fuel is being supplied to the engine. Once it warms up , and the choke is fully opened, the engine might be starving for fuel due to a low float level in the carburetor. Unleaded fuel caused a lot of problems causing the material on the float needle to swell and thereby shutting off addl fuel to the carb resulting in an insufficient quantity of fuel producing a lean condition where the engine would stumble when the accelerator is depressed. (Sometimes my tongue gets wrapped around my eye tooth and I can't see what I'm saying). If it was the accelerator pump it should happen cold and warmed up.
When the engine is cold the choke is partially closed and addl fuel is being supplied to the engine. Once it warms up , and the choke is fully opened, the engine might be starving for fuel due to a low float level in the carburetor. Unleaded fuel caused a lot of problems causing the material on the float needle to swell and thereby shutting off addl fuel to the carb resulting in an insufficient quantity of fuel producing a lean condition where the engine would stumble when the accelerator is depressed. (Sometimes my tongue gets wrapped around my eye tooth and I can't see what I'm saying). If it was the accelerator pump it should happen cold and warmed up.
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Joined: Jul 2006
Posts: 7,555
Engine stumble and or misfire/cut out reving it up,, bring up the RPMs in P/N in place?
All the vacuum lines and EGR intact? Stock?
If EGR flow is unregulated, or lines run incorrectly, thermal switches failed etc. it can apply full EGR flow causing unregulated exhaust into the intake stream. Possibly ingnition module or pick up, ignition related, but sounds like a lean condition as Hanky noted, or maybe EGR causing lean conditions.
Rich conditions,, it was common for the power valve under the front/bottom of the carb to leak and unmetered fuel would bleed down into the intake manifold. Same with a dried out old power valve ( if the truck has set for some time) was the diaphragm would dry out and get stiff, so the intake/carbs vacuum couldn't pull the power valve open enough or correctly for the right fuel drop causing lean conditions and poor drivability. Bottom of the bowl is also a good collection point for debris, could have a restriction there. If it still has an active EGR valve, unplug the vacuum line and see if it corrects.
If not, and if you can rev/raise the RPM's 'in place' in Park to duplicate the stumble , raise the RPM till it starts it stumble and manually close the choke in small increments. Improve?
If you start it cold, kick it down off of the fast idle and drive down the road, it runs good until fully warmed?
All the vacuum lines and EGR intact? Stock?
If EGR flow is unregulated, or lines run incorrectly, thermal switches failed etc. it can apply full EGR flow causing unregulated exhaust into the intake stream. Possibly ingnition module or pick up, ignition related, but sounds like a lean condition as Hanky noted, or maybe EGR causing lean conditions.
Rich conditions,, it was common for the power valve under the front/bottom of the carb to leak and unmetered fuel would bleed down into the intake manifold. Same with a dried out old power valve ( if the truck has set for some time) was the diaphragm would dry out and get stiff, so the intake/carbs vacuum couldn't pull the power valve open enough or correctly for the right fuel drop causing lean conditions and poor drivability. Bottom of the bowl is also a good collection point for debris, could have a restriction there. If it still has an active EGR valve, unplug the vacuum line and see if it corrects.
If not, and if you can rev/raise the RPM's 'in place' in Park to duplicate the stumble , raise the RPM till it starts it stumble and manually close the choke in small increments. Improve?
If you start it cold, kick it down off of the fast idle and drive down the road, it runs good until fully warmed?
Last edited by Hayapower; Feb 8, 2016 at 10:23 PM.
This is what I think could be taking place, and I could be wrong !
When the engine is cold the choke is partially closed and addl fuel is being supplied to the engine. Once it warms up , and the choke is fully opened, the engine might be starving for fuel due to a low float level in the carburetor. Unleaded fuel caused a lot of problems causing the material on the float needle to swell and thereby shutting off addl fuel to the carb resulting in an insufficient quantity of fuel producing a lean condition where the engine would stumble when the accelerator is depressed. (Sometimes my tongue gets wrapped around my eye tooth and I can't see what I'm saying). If it was the accelerator pump it should happen cold and warmed up.
When the engine is cold the choke is partially closed and addl fuel is being supplied to the engine. Once it warms up , and the choke is fully opened, the engine might be starving for fuel due to a low float level in the carburetor. Unleaded fuel caused a lot of problems causing the material on the float needle to swell and thereby shutting off addl fuel to the carb resulting in an insufficient quantity of fuel producing a lean condition where the engine would stumble when the accelerator is depressed. (Sometimes my tongue gets wrapped around my eye tooth and I can't see what I'm saying). If it was the accelerator pump it should happen cold and warmed up.
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