84 F150 Float height and metering rod adjustment
#1
11-16-2008, 09:25 PM
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84 F150 Float height and metering rod adjustment
Heyall!
My truck was sucking down the gas so I pulled the carb off to investigate.
This is the electronic feedback carb with the mixing solenoid and throttle position sensor, its the Carter YFA 1V.
I did find a big metal shaving in the main jet. Since I was rebuilding I reset the metering rod and the float dry height.
The way I found the float had the fuel level much higher than the recommendation on the rebuild cut sheet. I figured this for the reason why she was running richer (I also replaced the mixture control solenoid and that helped get me 7 miles more per gallon a few months ago.)
I also raised the metering rod just over an 1/8".
This was all done following cut sheet directions to a tee. I suspect the float or some other aspect of the carb is foreign and whoever previously tuned the carb knew what they were doing. The rig idled fine and then rough and then fine every few seconds so I pulled out the float and raised the float .1". This cleared that issue and it idles great. Accelerator pump shoots out a nice stream into the bore. Now, she craps out when I get up to 25mph in second. I assume my fuel level is still too low. When I took the carb out there was juice in the bowl though.
How do I dial in the fuel level and metering rod proper?
The main jet is stamped 120.
Any help GREATLY appreciated!
My truck was sucking down the gas so I pulled the carb off to investigate.
This is the electronic feedback carb with the mixing solenoid and throttle position sensor, its the Carter YFA 1V.
I did find a big metal shaving in the main jet. Since I was rebuilding I reset the metering rod and the float dry height.
The way I found the float had the fuel level much higher than the recommendation on the rebuild cut sheet. I figured this for the reason why she was running richer (I also replaced the mixture control solenoid and that helped get me 7 miles more per gallon a few months ago.)
I also raised the metering rod just over an 1/8".
This was all done following cut sheet directions to a tee. I suspect the float or some other aspect of the carb is foreign and whoever previously tuned the carb knew what they were doing. The rig idled fine and then rough and then fine every few seconds so I pulled out the float and raised the float .1". This cleared that issue and it idles great. Accelerator pump shoots out a nice stream into the bore. Now, she craps out when I get up to 25mph in second. I assume my fuel level is still too low. When I took the carb out there was juice in the bowl though.
How do I dial in the fuel level and metering rod proper?
The main jet is stamped 120.
Any help GREATLY appreciated!
#2
11-29-2008, 02:36 AM
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Just an update...
I drilled and tapped the hole over the metering rod adjustment screw.
A 1/4x20 plug with allen keyway fit in perfect.
Now, after driving a bit, I can pull over, lift off the air cleaner, take out the plug, and adjust the metering rod. I set the float back to .780, and 2.10 from the horn surface to the bottom of the hanging float.
Still no word on jets and metering rods.
Maybe someday I'll drop some cash on the JAW 14.7 wideband kit and really dial her in.
I drilled and tapped the hole over the metering rod adjustment screw.
A 1/4x20 plug with allen keyway fit in perfect.
Now, after driving a bit, I can pull over, lift off the air cleaner, take out the plug, and adjust the metering rod. I set the float back to .780, and 2.10 from the horn surface to the bottom of the hanging float.
Still no word on jets and metering rods.
Maybe someday I'll drop some cash on the JAW 14.7 wideband kit and really dial her in.
#3
11-29-2008, 08:45 AM
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Metering Rod Adjustment:
Back out the idle speed adjusting screw until the throttle plate is seated fully in its bore.
Press down on the upper end of the diaphragm shaft until the diaphragm bottoms in the vacuum chamber.
The metering rod should contact the bottom of the metering rod well and lifter link at the outer end nearest the springs and at the supporting link. The eyelet of the rod should slide freely on the pin of the metering rod arm.
On models not equipped with an adjusting screw, adjust by bending the metering rod pin tab.
On models with an adjusting screw, turn the screw until the metering rod just bottoms in the body casting. For final adjustment, turn the screw one additional turn clockwise.
Keep in mind also you might have a generic/cheap rebuild kit for the carb which may be wrong.
The fuel valve used for the 938 series carburetors was part number 25-190S with an orifice of 0.076 inch. The more common YF (used on Chevrolet and Ford) used orifices from 0.093 to 0.101 inch. Do the math with the equation for area on these and you can understand why many experience flooding problems. The YF as used on the Jeep will take 5-1/2 pounds pressure if the proper fuel valve is used. Many repair kits of today have too large an orifice. The larger orifice requires more buoyancy from the float (at idle), resulting in flooding and the need for a fuel pressure regulator.
Also, the correct fuel valve for the 938 series was spring-loaded. This fuel valve was developed by Carter for use on 'rough service' carburetors (off-road and marine). Its function was to smooth the jolting of the float, maintaining a more constant fuel level in the bowl, and minimizing damage to the float. If the truck is used only on the streets and highways, the replacement solid valve will suffice; however off-road trucks should use the spring-loaded fuel valve.
If you have done any engine modifications like a cam, intake or exhaust you probably need to change the metering rods as well. These Carter carbs were not known for being tolerant of any engine performance changes.
Can't help you with jets. An exhaust gas analizer would be the easiest to determine if you need to go up or down, but they are not exactly cheap or small.
Back out the idle speed adjusting screw until the throttle plate is seated fully in its bore.
Press down on the upper end of the diaphragm shaft until the diaphragm bottoms in the vacuum chamber.
The metering rod should contact the bottom of the metering rod well and lifter link at the outer end nearest the springs and at the supporting link. The eyelet of the rod should slide freely on the pin of the metering rod arm.
On models not equipped with an adjusting screw, adjust by bending the metering rod pin tab.
On models with an adjusting screw, turn the screw until the metering rod just bottoms in the body casting. For final adjustment, turn the screw one additional turn clockwise.
Keep in mind also you might have a generic/cheap rebuild kit for the carb which may be wrong.
The fuel valve used for the 938 series carburetors was part number 25-190S with an orifice of 0.076 inch. The more common YF (used on Chevrolet and Ford) used orifices from 0.093 to 0.101 inch. Do the math with the equation for area on these and you can understand why many experience flooding problems. The YF as used on the Jeep will take 5-1/2 pounds pressure if the proper fuel valve is used. Many repair kits of today have too large an orifice. The larger orifice requires more buoyancy from the float (at idle), resulting in flooding and the need for a fuel pressure regulator.
Also, the correct fuel valve for the 938 series was spring-loaded. This fuel valve was developed by Carter for use on 'rough service' carburetors (off-road and marine). Its function was to smooth the jolting of the float, maintaining a more constant fuel level in the bowl, and minimizing damage to the float. If the truck is used only on the streets and highways, the replacement solid valve will suffice; however off-road trucks should use the spring-loaded fuel valve.
If you have done any engine modifications like a cam, intake or exhaust you probably need to change the metering rods as well. These Carter carbs were not known for being tolerant of any engine performance changes.
Can't help you with jets. An exhaust gas analizer would be the easiest to determine if you need to go up or down, but they are not exactly cheap or small.
Last edited by Colorado Osprey; 11-29-2008 at 08:57 AM.